add tests

.gitea/workflows/test.yml

@@ -0,0 +1,87 @@
+name: Tests
+on:
+  push:
+    branches:
+      - master
+      - develop
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  test:
+    name: Run Tests
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '9.0.x'
+
+      - name: Restore dependencies
+        run: dotnet restore --verbosity normal
+
+      - name: Build solution
+        run: dotnet build --no-restore --verbosity normal
+
+      - name: Run unit tests
+        run: dotnet test --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults
+
+      - name: Generate test report
+        if: always()
+        run: |
+          echo "Test results:"
+          find ./TestResults -name "*.trx" -exec echo "Found test result file: {}" \;
+          find ./TestResults -name "*.xml" -exec echo "Found coverage file: {}" \;
+
+      - name: Upload test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-results
+          path: ./TestResults/
+          retention-days: 30
+
+  test-windows:
+    name: Run Tests (Windows)
+    runs-on: windows-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '9.0.x'
+
+      - name: Restore dependencies
+        run: dotnet restore --verbosity normal
+
+      - name: Build solution
+        run: dotnet build --no-restore --verbosity normal
+
+      - name: Run unit tests
+        run: dotnet test --no-build --verbosity normal --collect:"XPlat Code Coverage" --results-directory ./TestResults
+
+      - name: Generate test report
+        if: always()
+        run: |
+          echo "Test results:"
+          Get-ChildItem -Path ./TestResults -Recurse -Filter "*.trx" | ForEach-Object { Write-Host "Found test result file: $($_.FullName)" }
+          Get-ChildItem -Path ./TestResults -Recurse -Filter "*.xml" | ForEach-Object { Write-Host "Found coverage file: $($_.FullName)" }
+
+      - name: Upload test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-results-windows
+          path: ./TestResults/
+          retention-days: 30

ChatBot.Tests/ChatBot.Tests.csproj

@@ -0,0 +1,39 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.0" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="FluentAssertions" Version="8.7.1" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="9.0.10" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Options" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Configuration" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="9.0.10" />
+    <PackageReference Include="Telegram.Bot" Version="22.7.2" />
+    <PackageReference Include="OllamaSharp" Version="5.4.7" />
+    <PackageReference Include="FluentValidation" Version="12.0.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\ChatBot\ChatBot.csproj" />
+  </ItemGroup>
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+</Project>

ChatBot.Tests/Configuration/Validators/AISettingsValidatorTests.cs

@@ -0,0 +1,163 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Configuration.Validators;
+using FluentAssertions;
+
+namespace ChatBot.Tests.Configuration.Validators;
+
+public class AISettingsValidatorTests
+{
+    private readonly AISettingsValidator _validator = new();
+
+    [Fact]
+    public void Validate_ShouldReturnSuccess_WhenSettingsAreValid()
+    {
+        // Arrange
+        var settings = new AISettings
+        {
+            Temperature = 0.7,
+            SystemPromptPath = "Prompts/system-prompt.txt",
+            MaxRetryAttempts = 3,
+            RetryDelayMs = 1000,
+            MaxRetryDelayMs = 10000,
+            EnableExponentialBackoff = true,
+            RequestTimeoutSeconds = 30,
+            EnableHistoryCompression = true,
+            CompressionThreshold = 10,
+            CompressionTarget = 5,
+            MinMessageLengthForSummarization = 50,
+            MaxSummarizedMessageLength = 200,
+            CompressionTimeoutSeconds = 15,
+            StatusCheckTimeoutSeconds = 5,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeTrue();
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenTemperatureIsInvalid()
+    {
+        // Arrange
+        var settings = new AISettings
+        {
+            Temperature = 3.0, // Invalid: > 2.0
+            SystemPromptPath = "Prompts/system-prompt.txt",
+            MaxRetryAttempts = 3,
+            RetryDelayMs = 1000,
+            MaxRetryDelayMs = 10000,
+            EnableExponentialBackoff = true,
+            RequestTimeoutSeconds = 30,
+            EnableHistoryCompression = true,
+            CompressionThreshold = 10,
+            CompressionTarget = 5,
+            MinMessageLengthForSummarization = 50,
+            MaxSummarizedMessageLength = 200,
+            CompressionTimeoutSeconds = 15,
+            StatusCheckTimeoutSeconds = 5,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result
+            .Failures.Should()
+            .Contain(f => f.Contains("Temperature must be between 0.0 and 2.0"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenSystemPromptPathIsEmpty()
+    {
+        // Arrange
+        var settings = new AISettings
+        {
+            Temperature = 0.7,
+            SystemPromptPath = "", // Invalid: empty
+            MaxRetryAttempts = 3,
+            RetryDelayMs = 1000,
+            MaxRetryDelayMs = 10000,
+            EnableExponentialBackoff = true,
+            RequestTimeoutSeconds = 30,
+            EnableHistoryCompression = true,
+            CompressionThreshold = 10,
+            CompressionTarget = 5,
+            MinMessageLengthForSummarization = 50,
+            MaxSummarizedMessageLength = 200,
+            CompressionTimeoutSeconds = 15,
+            StatusCheckTimeoutSeconds = 5,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("System prompt path cannot be empty"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenMaxRetryAttemptsIsInvalid()
+    {
+        // Arrange
+        var settings = new AISettings
+        {
+            Temperature = 0.7,
+            SystemPromptPath = "Prompts/system-prompt.txt",
+            MaxRetryAttempts = 15, // Invalid: > 10
+            RetryDelayMs = 1000,
+            MaxRetryDelayMs = 10000,
+            EnableExponentialBackoff = true,
+            RequestTimeoutSeconds = 30,
+            EnableHistoryCompression = true,
+            CompressionThreshold = 10,
+            CompressionTarget = 5,
+            MinMessageLengthForSummarization = 50,
+            MaxSummarizedMessageLength = 200,
+            CompressionTimeoutSeconds = 15,
+            StatusCheckTimeoutSeconds = 5,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Max retry attempts cannot exceed 10"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenCompressionSettingsAreInvalid()
+    {
+        // Arrange
+        var settings = new AISettings
+        {
+            Temperature = 0.7,
+            SystemPromptPath = "Prompts/system-prompt.txt",
+            MaxRetryAttempts = 3,
+            RetryDelayMs = 1000,
+            MaxRetryDelayMs = 10000,
+            EnableExponentialBackoff = true,
+            RequestTimeoutSeconds = 30,
+            EnableHistoryCompression = true,
+            CompressionThreshold = 5, // Invalid: same as target
+            CompressionTarget = 5,
+            MinMessageLengthForSummarization = 50,
+            MaxSummarizedMessageLength = 200,
+            CompressionTimeoutSeconds = 15,
+            StatusCheckTimeoutSeconds = 5,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result
+            .Failures.Should()
+            .Contain(f => f.Contains("Compression target must be less than compression threshold"));
+    }
+}

ChatBot.Tests/Configuration/Validators/DatabaseSettingsValidatorTests.cs

@@ -0,0 +1,92 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Configuration.Validators;
+using FluentAssertions;
+
+namespace ChatBot.Tests.Configuration.Validators;
+
+public class DatabaseSettingsValidatorTests
+{
+    private readonly DatabaseSettingsValidator _validator = new();
+
+    [Fact]
+    public void Validate_ShouldReturnSuccess_WhenSettingsAreValid()
+    {
+        // Arrange
+        var settings = new DatabaseSettings
+        {
+            ConnectionString =
+                "Host=localhost;Port=5432;Database=chatbot;Username=user;Password=pass",
+            CommandTimeout = 30,
+            EnableSensitiveDataLogging = false,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeTrue();
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenConnectionStringIsEmpty()
+    {
+        // Arrange
+        var settings = new DatabaseSettings
+        {
+            ConnectionString = "",
+            CommandTimeout = 30,
+            EnableSensitiveDataLogging = false,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Database connection string is required"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenCommandTimeoutIsInvalid()
+    {
+        // Arrange
+        var settings = new DatabaseSettings
+        {
+            ConnectionString =
+                "Host=localhost;Port=5432;Database=chatbot;Username=user;Password=pass",
+            CommandTimeout = 0, // Invalid: <= 0
+            EnableSensitiveDataLogging = false,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Command timeout must be greater than 0"));
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void Validate_ShouldReturnFailure_WhenConnectionStringIsNullOrWhitespace(
+        string? connectionString
+    )
+    {
+        // Arrange
+        var settings = new DatabaseSettings
+        {
+            ConnectionString = connectionString!,
+            CommandTimeout = 30,
+            EnableSensitiveDataLogging = false,
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Database connection string is required"));
+    }
+}

ChatBot.Tests/Configuration/Validators/OllamaSettingsValidatorTests.cs

@@ -0,0 +1,86 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Configuration.Validators;
+using FluentAssertions;
+
+namespace ChatBot.Tests.Configuration.Validators;
+
+public class OllamaSettingsValidatorTests
+{
+    private readonly OllamaSettingsValidator _validator = new();
+
+    [Fact]
+    public void Validate_ShouldReturnSuccess_WhenSettingsAreValid()
+    {
+        // Arrange
+        var settings = new OllamaSettings
+        {
+            Url = "http://localhost:11434",
+            DefaultModel = "llama3.2",
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeTrue();
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenUrlIsEmpty()
+    {
+        // Arrange
+        var settings = new OllamaSettings { Url = "", DefaultModel = "llama3.2" };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Ollama URL is required"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenUrlIsInvalid()
+    {
+        // Arrange
+        var settings = new OllamaSettings { Url = "invalid-url", DefaultModel = "llama3.2" };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Invalid Ollama URL format"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenDefaultModelIsEmpty()
+    {
+        // Arrange
+        var settings = new OllamaSettings { Url = "http://localhost:11434", DefaultModel = "" };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("DefaultModel is required"));
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void Validate_ShouldReturnFailure_WhenUrlIsNullOrWhitespace(string? url)
+    {
+        // Arrange
+        var settings = new OllamaSettings { Url = url!, DefaultModel = "llama3.2" };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Ollama URL is required"));
+    }
+}

ChatBot.Tests/Configuration/Validators/TelegramBotSettingsValidatorTests.cs

@@ -0,0 +1,76 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Configuration.Validators;
+using FluentAssertions;
+
+namespace ChatBot.Tests.Configuration.Validators;
+
+public class TelegramBotSettingsValidatorTests
+{
+    private readonly TelegramBotSettingsValidator _validator = new();
+
+    [Fact]
+    public void Validate_ShouldReturnSuccess_WhenSettingsAreValid()
+    {
+        // Arrange
+        var settings = new TelegramBotSettings
+        {
+            BotToken = "1234567890:ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijk",
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeTrue();
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenBotTokenIsEmpty()
+    {
+        // Arrange
+        var settings = new TelegramBotSettings { BotToken = "" };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Telegram bot token is required"));
+    }
+
+    [Fact]
+    public void Validate_ShouldReturnFailure_WhenBotTokenIsTooShort()
+    {
+        // Arrange
+        var settings = new TelegramBotSettings
+        {
+            BotToken = "1234567890:ABC", // 15 chars, too short
+        };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result
+            .Failures.Should()
+            .Contain(f => f.Contains("Telegram bot token must be at least 40 characters"));
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void Validate_ShouldReturnFailure_WhenBotTokenIsNullOrWhitespace(string? botToken)
+    {
+        // Arrange
+        var settings = new TelegramBotSettings { BotToken = botToken! };
+
+        // Act
+        var result = _validator.Validate(null, settings);
+
+        // Assert
+        result.Succeeded.Should().BeFalse();
+        result.Failures.Should().Contain(f => f.Contains("Telegram bot token is required"));
+    }
+}

ChatBot.Tests/Data/Repositories/ChatSessionRepositoryTests.cs

@@ -0,0 +1,266 @@
+using ChatBot.Data;
+using ChatBot.Data.Interfaces;
+using ChatBot.Data.Repositories;
+using ChatBot.Models.Entities;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Moq;
+
+namespace ChatBot.Tests.Data.Repositories;
+
+public class ChatSessionRepositoryTests : TestBase
+{
+    private ChatBotDbContext _dbContext = null!;
+    private ChatSessionRepository _repository = null!;
+
+    public ChatSessionRepositoryTests()
+    {
+        SetupServices();
+    }
+
+    protected override void ConfigureServices(IServiceCollection services)
+    {
+        // Add in-memory database with unique name per test
+        services.AddDbContext<ChatBotDbContext>(options =>
+            options.UseInMemoryDatabase(Guid.NewGuid().ToString())
+        );
+
+        // Add logger
+        services.AddSingleton(Mock.Of<ILogger<ChatSessionRepository>>());
+
+        // Add repository
+        services.AddScoped<IChatSessionRepository, ChatSessionRepository>();
+    }
+
+    protected override void SetupServices()
+    {
+        base.SetupServices();
+
+        _dbContext = ServiceProvider.GetRequiredService<ChatBotDbContext>();
+        _repository = (ChatSessionRepository)
+            ServiceProvider.GetRequiredService<IChatSessionRepository>();
+
+        // Ensure database is created
+        _dbContext.Database.EnsureCreated();
+    }
+
+    private void CleanupDatabase()
+    {
+        _dbContext.ChatSessions.RemoveRange(_dbContext.ChatSessions);
+        _dbContext.ChatMessages.RemoveRange(_dbContext.ChatMessages);
+        _dbContext.SaveChanges();
+    }
+
+    [Fact]
+    public async Task GetOrCreateAsync_ShouldReturnExistingSession_WhenSessionExists()
+    {
+        // Arrange
+        CleanupDatabase();
+        var chatId = 12345L;
+        var chatType = "private";
+        var chatTitle = "Test Chat";
+
+        var existingSession = TestDataBuilder.Mocks.CreateChatSessionEntity(
+            1,
+            chatId,
+            "existing-session",
+            chatType,
+            chatTitle
+        );
+        _dbContext.ChatSessions.Add(existingSession);
+        await _dbContext.SaveChangesAsync();
+
+        // Act
+        var result = await _repository.GetOrCreateAsync(chatId, chatType, chatTitle);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(chatId);
+        result.SessionId.Should().Be("existing-session");
+    }
+
+    [Fact]
+    public async Task GetOrCreateAsync_ShouldCreateNewSession_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        CleanupDatabase();
+        var chatId = 12345L;
+        var chatType = "private";
+        var chatTitle = "Test Chat";
+
+        // Act
+        var result = await _repository.GetOrCreateAsync(chatId, chatType, chatTitle);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(chatId);
+        result.ChatType.Should().Be(chatType);
+        result.ChatTitle.Should().Be(chatTitle);
+        result.SessionId.Should().NotBeNullOrEmpty();
+    }
+
+    [Fact]
+    public async Task GetByChatIdAsync_ShouldReturnSession_WhenSessionExists()
+    {
+        // Arrange
+        CleanupDatabase();
+        var chatId = 12345L;
+        var session = TestDataBuilder.Mocks.CreateChatSessionEntity(1, chatId);
+        _dbContext.ChatSessions.Add(session);
+        await _dbContext.SaveChangesAsync();
+
+        // Act
+        var result = await _repository.GetByChatIdAsync(chatId);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(chatId);
+    }
+
+    [Fact]
+    public async Task GetByChatIdAsync_ShouldReturnNull_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        CleanupDatabase();
+        var chatId = 12345L;
+
+        // Act
+        var result = await _repository.GetByChatIdAsync(chatId);
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task GetBySessionIdAsync_ShouldReturnSession_WhenSessionExists()
+    {
+        // Arrange
+        CleanupDatabase();
+        var sessionId = "test-session";
+        var session = TestDataBuilder.Mocks.CreateChatSessionEntity(1, 12345, sessionId);
+        _dbContext.ChatSessions.Add(session);
+        await _dbContext.SaveChangesAsync();
+
+        // Act
+        var result = await _repository.GetBySessionIdAsync(sessionId);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.SessionId.Should().Be(sessionId);
+    }
+
+    [Fact]
+    public async Task GetBySessionIdAsync_ShouldReturnNull_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        CleanupDatabase();
+        var sessionId = "nonexistent-session";
+
+        // Act
+        var result = await _repository.GetBySessionIdAsync(sessionId);
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task UpdateAsync_ShouldUpdateSession()
+    {
+        // Arrange
+        CleanupDatabase();
+        var session = TestDataBuilder.Mocks.CreateChatSessionEntity(1, 12345);
+        _dbContext.ChatSessions.Add(session);
+        await _dbContext.SaveChangesAsync();
+
+        session.ChatTitle = "Updated Title";
+
+        // Act
+        var result = await _repository.UpdateAsync(session);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatTitle.Should().Be("Updated Title");
+    }
+
+    [Fact]
+    public async Task DeleteAsync_ShouldReturnTrue_WhenSessionExists()
+    {
+        // Arrange
+        CleanupDatabase();
+        var chatId = 12345L;
+        var session = TestDataBuilder.Mocks.CreateChatSessionEntity(1, chatId);
+        _dbContext.ChatSessions.Add(session);
+        await _dbContext.SaveChangesAsync();
+
+        // Act
+        var result = await _repository.DeleteAsync(chatId);
+
+        // Assert
+        result.Should().BeTrue();
+        var deletedSession = await _repository.GetByChatIdAsync(chatId);
+        deletedSession.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task DeleteAsync_ShouldReturnFalse_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        CleanupDatabase();
+        var chatId = 12345L;
+
+        // Act
+        var result = await _repository.DeleteAsync(chatId);
+
+        // Assert
+        result.Should().BeFalse();
+    }
+
+    [Fact]
+    public async Task GetActiveSessionsCountAsync_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        CleanupDatabase();
+        var session1 = TestDataBuilder.Mocks.CreateChatSessionEntity(1, 12345);
+        var session2 = TestDataBuilder.Mocks.CreateChatSessionEntity(2, 12346);
+        _dbContext.ChatSessions.AddRange(session1, session2);
+        await _dbContext.SaveChangesAsync();
+
+        // Act
+        var count = await _repository.GetActiveSessionsCountAsync();
+
+        // Assert
+        count.Should().Be(2);
+    }
+
+    [Fact]
+    public async Task CleanupOldSessionsAsync_ShouldRemoveOldSessions()
+    {
+        // Arrange
+        CleanupDatabase();
+
+        // Verify database is empty
+        var initialCount = await _repository.GetActiveSessionsCountAsync();
+        initialCount.Should().Be(0);
+
+        var oldSession = TestDataBuilder.Mocks.CreateChatSessionEntity(1, 12345);
+        oldSession.LastUpdatedAt = DateTime.UtcNow.AddDays(-2); // 2 days old
+
+        var recentSession = TestDataBuilder.Mocks.CreateChatSessionEntity(2, 12346);
+        recentSession.LastUpdatedAt = DateTime.UtcNow.AddMinutes(-30); // 30 minutes old
+
+        _dbContext.ChatSessions.AddRange(oldSession, recentSession);
+        await _dbContext.SaveChangesAsync();
+
+        // Act
+        var removedCount = await _repository.CleanupOldSessionsAsync(1); // Remove sessions older than 1 hour
+
+        // Assert
+        removedCount.Should().Be(1);
+        var remainingSessions = await _repository.GetActiveSessionsCountAsync();
+        remainingSessions.Should().Be(1);
+    }
+}

ChatBot.Tests/Integration/ChatServiceIntegrationTests.cs

@@ -0,0 +1,246 @@
+using System.Linq;
+using ChatBot.Models;
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Dto;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using OllamaSharp.Models.Chat;
+
+namespace ChatBot.Tests.Integration;
+
+public class ChatServiceIntegrationTests : TestBase
+{
+    private ChatService _chatService = null!;
+    private Mock<ISessionStorage> _sessionStorageMock = null!;
+    private Mock<IAIService> _aiServiceMock = null!;
+
+    public ChatServiceIntegrationTests()
+    {
+        SetupServices();
+    }
+
+    protected override void ConfigureServices(IServiceCollection services)
+    {
+        // Add mocked services
+        _sessionStorageMock = TestDataBuilder.Mocks.CreateSessionStorageMock();
+        _aiServiceMock = TestDataBuilder.Mocks.CreateAIServiceMock();
+
+        services.AddSingleton(_sessionStorageMock.Object);
+        services.AddSingleton(_aiServiceMock.Object);
+        services.AddSingleton(Mock.Of<ILogger<ChatService>>());
+        services.AddSingleton(
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object
+        );
+        services.AddSingleton(TestDataBuilder.Mocks.CreateCompressionServiceMock().Object);
+        services.AddScoped<ChatService>();
+    }
+
+    protected override void SetupServices()
+    {
+        base.SetupServices();
+        _chatService = ServiceProvider.GetRequiredService<ChatService>();
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldProcessUserMessage_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello, how are you?";
+        var expectedResponse = "I'm doing well, thank you!";
+
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(chatId);
+        _sessionStorageMock.Setup(x => x.GetOrCreate(chatId, "private", "")).Returns(session);
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(expectedResponse);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        session.GetAllMessages().Should().HaveCount(2); // User message + AI response
+        session.GetAllMessages()[0].Content.Should().Be(message);
+        session.GetAllMessages()[0].Role.Should().Be(ChatRole.User);
+        session.GetAllMessages()[1].Content.Should().Be(expectedResponse);
+        session.GetAllMessages()[1].Role.Should().Be(ChatRole.Assistant);
+
+        _sessionStorageMock.Verify(x => x.SaveSessionAsync(session), Times.Exactly(2));
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldCreateNewSession_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello";
+        var expectedResponse = "Hi there!";
+
+        _sessionStorageMock
+            .Setup(x => x.GetOrCreate(chatId, "private", ""))
+            .Returns(TestDataBuilder.ChatSessions.CreateBasicSession(chatId));
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(expectedResponse);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        _sessionStorageMock.Verify(x => x.GetOrCreate(chatId, "private", ""), Times.Once);
+        _sessionStorageMock.Verify(
+            x => x.SaveSessionAsync(It.IsAny<ChatBot.Models.ChatSession>()),
+            Times.Exactly(2)
+        );
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldHandleEmptyMessage()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "";
+        var expectedResponse = "I didn't receive a message. Could you please try again?";
+
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(chatId);
+        _sessionStorageMock.Setup(x => x.GetOrCreate(chatId, "private", "")).Returns(session);
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(expectedResponse);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        session.GetAllMessages().Should().HaveCount(2);
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldHandleAIServiceException()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello";
+
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(chatId);
+        _sessionStorageMock.Setup(x => x.GetOrCreate(chatId, "private", "")).Returns(session);
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ThrowsAsync(new Exception("AI service error"));
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert - should return error message instead of throwing
+        result.Should().Contain("ошибка");
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldUseCompression_WhenEnabled()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello";
+        var expectedResponse = "Hi there!";
+
+        var session = TestDataBuilder.ChatSessions.CreateSessionWithMessages(chatId, 10); // 10 messages
+        _sessionStorageMock.Setup(x => x.GetOrCreate(chatId, "private", "")).Returns(session);
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(expectedResponse);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        _aiServiceMock.Verify(
+            x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                ),
+            Times.Once
+        );
+    }
+
+    [Fact]
+    public async Task ClearHistoryAsync_ShouldClearSessionMessages()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var session = TestDataBuilder.ChatSessions.CreateSessionWithMessages(chatId, 5);
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns(session);
+
+        // Act
+        await _chatService.ClearHistoryAsync(chatId);
+
+        // Assert
+        session.GetAllMessages().Should().BeEmpty();
+        _sessionStorageMock.Verify(x => x.SaveSessionAsync(session), Times.Once);
+    }
+
+    [Fact]
+    public async Task ClearHistoryAsync_ShouldHandleNonExistentSession()
+    {
+        // Arrange
+        var chatId = 12345L;
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns((ChatBot.Models.ChatSession?)null);
+
+        // Act
+        await _chatService.ClearHistoryAsync(chatId);
+
+        // Assert
+        _sessionStorageMock.Verify(
+            x => x.SaveSessionAsync(It.IsAny<ChatBot.Models.ChatSession>()),
+            Times.Never
+        );
+    }
+}

ChatBot.Tests/Models/ChatSessionTests.cs

@@ -0,0 +1,186 @@
+using ChatBot.Models;
+using ChatBot.Models.Dto;
+using FluentAssertions;
+using OllamaSharp.Models.Chat;
+
+namespace ChatBot.Tests.Models;
+
+public class ChatSessionTests
+{
+    [Fact]
+    public void Constructor_ShouldInitializeProperties()
+    {
+        // Arrange & Act
+        var session = new ChatSession();
+
+        // Assert
+        session.ChatId.Should().Be(0);
+        session.SessionId.Should().NotBeNullOrEmpty();
+        session.ChatType.Should().Be("private");
+        session.ChatTitle.Should().Be(string.Empty);
+        session.Model.Should().Be(string.Empty);
+        session.CreatedAt.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromSeconds(1));
+        session.LastUpdatedAt.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromSeconds(1));
+        session.GetAllMessages().Should().NotBeNull();
+        session.GetAllMessages().Should().BeEmpty();
+    }
+
+    [Fact]
+    public void AddUserMessage_ShouldAddMessageToSession()
+    {
+        // Arrange
+        var session = new ChatSession();
+        var content = "Hello";
+        var username = "testuser";
+
+        // Act
+        session.AddUserMessage(content, username);
+
+        // Assert
+        session.GetAllMessages().Should().HaveCount(1);
+        var message = session.GetAllMessages().First();
+        message.Role.Should().Be(ChatRole.User);
+        message.Content.Should().Be(content);
+    }
+
+    [Fact]
+    public void AddAssistantMessage_ShouldAddMessageToSession()
+    {
+        // Arrange
+        var session = new ChatSession();
+        var content = "Hello! How can I help you?";
+
+        // Act
+        session.AddAssistantMessage(content);
+
+        // Assert
+        session.GetAllMessages().Should().HaveCount(1);
+        var message = session.GetAllMessages().First();
+        message.Role.Should().Be(ChatRole.Assistant);
+        message.Content.Should().Be(content);
+    }
+
+    [Fact]
+    public void AddMessage_ShouldAddMessageToSession()
+    {
+        // Arrange
+        var session = new ChatSession();
+        var content = "You are a helpful assistant.";
+        var message = new ChatMessage { Role = ChatRole.System, Content = content };
+
+        // Act
+        session.AddMessage(message);
+
+        // Assert
+        session.GetAllMessages().Should().HaveCount(1);
+        var addedMessage = session.GetAllMessages().First();
+        addedMessage.Role.Should().Be(ChatRole.System);
+        addedMessage.Content.Should().Be(content);
+    }
+
+    [Fact]
+    public void ClearHistory_ShouldRemoveAllMessages()
+    {
+        // Arrange
+        var session = new ChatSession();
+        session.AddUserMessage("Hello", "testuser");
+        session.AddAssistantMessage("Hi there!");
+
+        // Act
+        session.ClearHistory();
+
+        // Assert
+        session.GetAllMessages().Should().BeEmpty();
+    }
+
+    [Fact]
+    public void GetMessageCount_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        var session = new ChatSession();
+        session.AddUserMessage("Hello", "testuser");
+        session.AddAssistantMessage("Hi there!");
+        session.AddUserMessage("How are you?", "testuser");
+
+        // Act
+        var count = session.GetMessageCount();
+
+        // Assert
+        count.Should().Be(3);
+    }
+
+    [Fact]
+    public void GetLastMessage_ShouldReturnLastMessage()
+    {
+        // Arrange
+        var session = new ChatSession();
+        session.AddUserMessage("Hello", "testuser");
+        session.AddAssistantMessage("Hi there!");
+        session.AddUserMessage("How are you?", "testuser");
+
+        // Act
+        var messages = session.GetAllMessages();
+        var lastMessage = messages.LastOrDefault();
+
+        // Assert
+        lastMessage.Should().NotBeNull();
+        lastMessage!.Content.Should().Be("How are you?");
+        lastMessage.Role.Should().Be(ChatRole.User);
+    }
+
+    [Fact]
+    public void GetLastMessage_ShouldReturnNull_WhenNoMessages()
+    {
+        // Arrange
+        var session = new ChatSession();
+
+        // Act
+        var messages = session.GetAllMessages();
+        var lastMessage = messages.LastOrDefault();
+
+        // Assert
+        lastMessage.Should().BeNull();
+    }
+
+    [Fact]
+    public void AddMessage_ShouldUpdateLastUpdatedAt()
+    {
+        // Arrange
+        var session = new ChatSession();
+        var originalTime = session.LastUpdatedAt;
+        var message = new ChatMessage { Role = ChatRole.User, Content = "Test" };
+
+        // Act
+        session.AddMessage(message);
+
+        // Assert
+        session.LastUpdatedAt.Should().BeAfter(originalTime);
+    }
+
+    [Fact]
+    public void GetMessageCount_ShouldReturnZero_WhenNoMessages()
+    {
+        // Arrange
+        var session = new ChatSession();
+
+        // Act
+        var count = session.GetMessageCount();
+
+        // Assert
+        count.Should().Be(0);
+    }
+
+    [Fact]
+    public void GetMessageCount_ShouldReturnCorrectCount_WhenHasMessages()
+    {
+        // Arrange
+        var session = new ChatSession();
+        session.AddUserMessage("Hello", "testuser");
+
+        // Act
+        var count = session.GetMessageCount();
+
+        // Assert
+        count.Should().Be(1);
+    }
+}

ChatBot.Tests/Services/AIServiceTests.cs

@@ -0,0 +1,209 @@
+using System.Linq;
+using ChatBot.Common.Constants;
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Dto;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using OllamaSharp.Models.Chat;
+
+namespace ChatBot.Tests.Services;
+
+public class AIServiceTests : UnitTestBase
+{
+    private readonly Mock<ILogger<AIService>> _loggerMock;
+    private readonly Mock<ModelService> _modelServiceMock;
+    private readonly Mock<IOllamaClient> _ollamaClientMock;
+    private readonly Mock<SystemPromptService> _systemPromptServiceMock;
+    private readonly Mock<IHistoryCompressionService> _compressionServiceMock;
+    private readonly AISettings _aiSettings;
+    private readonly AIService _aiService;
+
+    public AIServiceTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<AIService>();
+        var ollamaSettings = TestDataBuilder.Configurations.CreateOllamaSettings();
+        var ollamaOptionsMock = TestDataBuilder.Mocks.CreateOptionsMock(ollamaSettings);
+        _modelServiceMock = new Mock<ModelService>(
+            Mock.Of<ILogger<ModelService>>(),
+            ollamaOptionsMock.Object
+        );
+        _ollamaClientMock = TestDataBuilder.Mocks.CreateOllamaClientMock();
+        _systemPromptServiceMock = new Mock<SystemPromptService>(
+            Mock.Of<ILogger<SystemPromptService>>(),
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object
+        );
+        _compressionServiceMock = TestDataBuilder.Mocks.CreateCompressionServiceMock();
+        _aiSettings = TestDataBuilder.Configurations.CreateAISettings();
+
+        var optionsMock = TestDataBuilder.Mocks.CreateOptionsMock(_aiSettings);
+
+        _aiService = new AIService(
+            _loggerMock.Object,
+            _modelServiceMock.Object,
+            _ollamaClientMock.Object,
+            optionsMock.Object,
+            _systemPromptServiceMock.Object,
+            _compressionServiceMock.Object
+        );
+    }
+
+    [Fact]
+    public async Task GenerateChatCompletionAsync_ShouldReturnResponse_WhenSuccessful()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(2);
+        var expectedResponse = "Test AI response";
+        var model = "llama3.2";
+
+        _modelServiceMock.Setup(x => x.GetCurrentModel()).Returns(model);
+        _systemPromptServiceMock.Setup(x => x.GetSystemPromptAsync()).ReturnsAsync("System prompt");
+
+        var responseBuilder = new System.Text.StringBuilder();
+        responseBuilder.Append(expectedResponse);
+
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(
+                TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
+                    {
+                        new OllamaSharp.Models.Chat.ChatResponseStream
+                        {
+                            Message = new Message(ChatRole.Assistant, expectedResponse),
+                        },
+                    }
+                )
+            );
+
+        // Act
+        var result = await _aiService.GenerateChatCompletionAsync(messages);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        _ollamaClientMock.Verify(
+            x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()),
+            Times.Once
+        );
+    }
+
+    [Fact]
+    public async Task GenerateChatCompletionAsync_ShouldThrowException_WhenOllamaClientThrows()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(2);
+        var model = "llama3.2";
+
+        _modelServiceMock.Setup(x => x.GetCurrentModel()).Returns(model);
+        _systemPromptServiceMock.Setup(x => x.GetSystemPromptAsync()).ReturnsAsync("System prompt");
+
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Throws(new Exception("Ollama client error"));
+
+        // Act & Assert
+        var result = await _aiService.GenerateChatCompletionAsync(messages);
+        result.Should().Be(AIResponseConstants.DefaultErrorMessage);
+    }
+
+    [Fact]
+    public async Task GenerateChatCompletionWithCompressionAsync_ShouldUseCompression_WhenEnabled()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(10);
+        var expectedResponse = "Test AI response with compression";
+        var model = "llama3.2";
+
+        _modelServiceMock.Setup(x => x.GetCurrentModel()).Returns(model);
+        _systemPromptServiceMock.Setup(x => x.GetSystemPromptAsync()).ReturnsAsync("System prompt");
+        _compressionServiceMock.Setup(x => x.ShouldCompress(20, 10)).Returns(true);
+        _compressionServiceMock
+            .Setup(x =>
+                x.CompressHistoryAsync(
+                    It.IsAny<List<ChatMessage>>(),
+                    5,
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(messages.TakeLast(5).ToList());
+
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(
+                TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
+                    {
+                        new OllamaSharp.Models.Chat.ChatResponseStream
+                        {
+                            Message = new Message(ChatRole.Assistant, expectedResponse),
+                        },
+                    }
+                )
+            );
+
+        // Act
+        var result = await _aiService.GenerateChatCompletionWithCompressionAsync(messages);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        _compressionServiceMock.Verify(x => x.ShouldCompress(20, 10), Times.Once);
+        _compressionServiceMock.Verify(
+            x =>
+                x.CompressHistoryAsync(
+                    It.IsAny<List<ChatMessage>>(),
+                    5,
+                    It.IsAny<CancellationToken>()
+                ),
+            Times.Once
+        );
+    }
+
+    [Fact]
+    public async Task GenerateChatCompletionWithCompressionAsync_ShouldNotUseCompression_WhenNotNeeded()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(3);
+        var expectedResponse = "Test AI response without compression";
+        var model = "llama3.2";
+
+        _modelServiceMock.Setup(x => x.GetCurrentModel()).Returns(model);
+        _systemPromptServiceMock.Setup(x => x.GetSystemPromptAsync()).ReturnsAsync("System prompt");
+        _compressionServiceMock.Setup(x => x.ShouldCompress(6, 10)).Returns(false);
+
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(
+                TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
+                    {
+                        new OllamaSharp.Models.Chat.ChatResponseStream
+                        {
+                            Message = new Message(ChatRole.Assistant, expectedResponse),
+                        },
+                    }
+                )
+            );
+
+        // Act
+        var result = await _aiService.GenerateChatCompletionWithCompressionAsync(messages);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        _compressionServiceMock.Verify(x => x.ShouldCompress(6, 10), Times.Once);
+        _compressionServiceMock.Verify(
+            x =>
+                x.CompressHistoryAsync(
+                    It.IsAny<List<ChatMessage>>(),
+                    It.IsAny<int>(),
+                    It.IsAny<CancellationToken>()
+                ),
+            Times.Never
+        );
+    }
+}

ChatBot.Tests/Services/ChatServiceTests.cs

@@ -0,0 +1,321 @@
+using ChatBot.Models;
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Dto;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+
+namespace ChatBot.Tests.Services;
+
+public class ChatServiceTests : UnitTestBase
+{
+    private readonly Mock<ILogger<ChatService>> _loggerMock;
+    private readonly Mock<IAIService> _aiServiceMock;
+    private readonly Mock<ISessionStorage> _sessionStorageMock;
+    private readonly Mock<IHistoryCompressionService> _compressionServiceMock;
+    private readonly AISettings _aiSettings;
+    private readonly ChatService _chatService;
+
+    public ChatServiceTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<ChatService>();
+        _aiServiceMock = TestDataBuilder.Mocks.CreateAIServiceMock();
+        _sessionStorageMock = TestDataBuilder.Mocks.CreateSessionStorageMock();
+        _compressionServiceMock = TestDataBuilder.Mocks.CreateCompressionServiceMock();
+        _aiSettings = TestDataBuilder.Configurations.CreateAISettings();
+
+        var optionsMock = TestDataBuilder.Mocks.CreateOptionsMock(_aiSettings);
+
+        _chatService = new ChatService(
+            _loggerMock.Object,
+            _aiServiceMock.Object,
+            _sessionStorageMock.Object,
+            optionsMock.Object,
+            _compressionServiceMock.Object
+        );
+    }
+
+    [Fact]
+    public void GetOrCreateSession_ShouldCreateNewSession_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var chatType = "private";
+        var chatTitle = "Test Chat";
+
+        // Act
+        var session = _chatService.GetOrCreateSession(chatId, chatType, chatTitle);
+
+        // Assert
+        session.Should().NotBeNull();
+        session.ChatId.Should().Be(chatId);
+        session.ChatType.Should().Be(chatType);
+        session.ChatTitle.Should().Be(chatTitle);
+
+        _sessionStorageMock.Verify(x => x.GetOrCreate(chatId, chatType, chatTitle), Times.Once);
+    }
+
+    [Fact]
+    public void GetOrCreateSession_ShouldSetCompressionService_WhenCompressionIsEnabled()
+    {
+        // Arrange
+        var chatId = 12345L;
+        _aiSettings.EnableHistoryCompression = true;
+
+        // Act
+        var session = _chatService.GetOrCreateSession(chatId);
+
+        // Assert
+        session.Should().NotBeNull();
+        _sessionStorageMock.Verify(x => x.GetOrCreate(chatId, "private", ""), Times.Once);
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldProcessMessageSuccessfully_WhenValidInput()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello, bot!";
+        var expectedResponse = "Hello! How can I help you?";
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(expectedResponse);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be(expectedResponse);
+        _sessionStorageMock.Verify(
+            x => x.SaveSessionAsync(It.IsAny<ChatBot.Models.ChatSession>()),
+            Times.AtLeastOnce
+        );
+        _aiServiceMock.Verify(
+            x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                ),
+            Times.Once
+        );
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldReturnEmptyString_WhenAIResponseIsEmptyMarker()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello, bot!";
+        var emptyResponse = "{empty}";
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync(emptyResponse);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldReturnErrorMessage_WhenAIResponseIsNull()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello, bot!";
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ReturnsAsync((string)null!);
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be("Извините, произошла ошибка при генерации ответа.");
+    }
+
+    [Fact]
+    public async Task ProcessMessageAsync_ShouldHandleException_WhenErrorOccurs()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var username = "testuser";
+        var message = "Hello, bot!";
+
+        _aiServiceMock
+            .Setup(x =>
+                x.GenerateChatCompletionWithCompressionAsync(
+                    It.IsAny<List<ChatBot.Models.Dto.ChatMessage>>(),
+                    It.IsAny<CancellationToken>()
+                )
+            )
+            .ThrowsAsync(new Exception("Test exception"));
+
+        // Act
+        var result = await _chatService.ProcessMessageAsync(chatId, username, message);
+
+        // Assert
+        result.Should().Be("Извините, произошла ошибка при обработке вашего сообщения.");
+        // Verify that error was logged
+        // In a real test, we would verify the logger calls
+    }
+
+    [Fact]
+    public async Task UpdateSessionParametersAsync_ShouldUpdateSession_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var newModel = "llama3.2";
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(chatId);
+
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns(session);
+
+        // Act
+        await _chatService.UpdateSessionParametersAsync(chatId, newModel);
+
+        // Assert
+        session.Model.Should().Be(newModel);
+        _sessionStorageMock.Verify(x => x.SaveSessionAsync(session), Times.Once);
+    }
+
+    [Fact]
+    public async Task UpdateSessionParametersAsync_ShouldNotUpdate_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var newModel = "llama3.2";
+
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns((ChatBot.Models.ChatSession?)null);
+
+        // Act
+        await _chatService.UpdateSessionParametersAsync(chatId, newModel);
+
+        // Assert
+        _sessionStorageMock.Verify(
+            x => x.SaveSessionAsync(It.IsAny<ChatBot.Models.ChatSession>()),
+            Times.Never
+        );
+    }
+
+    [Fact]
+    public async Task ClearHistoryAsync_ShouldClearHistory_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var session = TestDataBuilder.ChatSessions.CreateSessionWithMessages(chatId, 5);
+
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns(session);
+
+        // Act
+        await _chatService.ClearHistoryAsync(chatId);
+
+        // Assert
+        session.GetMessageCount().Should().Be(0);
+        _sessionStorageMock.Verify(x => x.SaveSessionAsync(session), Times.Once);
+    }
+
+    [Fact]
+    public void GetSession_ShouldReturnSession_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(chatId);
+
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns(session);
+
+        // Act
+        var result = _chatService.GetSession(chatId);
+
+        // Assert
+        result.Should().Be(session);
+    }
+
+    [Fact]
+    public void GetSession_ShouldReturnNull_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        var chatId = 12345L;
+
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns((ChatBot.Models.ChatSession?)null);
+
+        // Act
+        var result = _chatService.GetSession(chatId);
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public void RemoveSession_ShouldReturnTrue_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+
+        _sessionStorageMock.Setup(x => x.Remove(chatId)).Returns(true);
+
+        // Act
+        var result = _chatService.RemoveSession(chatId);
+
+        // Assert
+        result.Should().BeTrue();
+        _sessionStorageMock.Verify(x => x.Remove(chatId), Times.Once);
+    }
+
+    [Fact]
+    public void GetActiveSessionsCount_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        var expectedCount = 5;
+
+        _sessionStorageMock.Setup(x => x.GetActiveSessionsCount()).Returns(expectedCount);
+
+        // Act
+        var result = _chatService.GetActiveSessionsCount();
+
+        // Assert
+        result.Should().Be(expectedCount);
+    }
+
+    [Fact]
+    public void CleanupOldSessions_ShouldReturnCleanedCount()
+    {
+        // Arrange
+        var hoursOld = 24;
+        var expectedCleaned = 3;
+
+        _sessionStorageMock.Setup(x => x.CleanupOldSessions(hoursOld)).Returns(expectedCleaned);
+
+        // Act
+        var result = _chatService.CleanupOldSessions(hoursOld);
+
+        // Assert
+        result.Should().Be(expectedCleaned);
+        _sessionStorageMock.Verify(x => x.CleanupOldSessions(hoursOld), Times.Once);
+    }
+}

ChatBot.Tests/Services/DatabaseSessionStorageTests.cs

@@ -0,0 +1,182 @@
+using ChatBot.Data;
+using ChatBot.Data.Interfaces;
+using ChatBot.Data.Repositories;
+using ChatBot.Models;
+using ChatBot.Models.Entities;
+using ChatBot.Services;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Moq;
+
+namespace ChatBot.Tests.Services;
+
+public class DatabaseSessionStorageTests : TestBase
+{
+    private ChatBotDbContext _dbContext = null!;
+    private DatabaseSessionStorage _sessionStorage = null!;
+    private Mock<IChatSessionRepository> _repositoryMock = null!;
+
+    public DatabaseSessionStorageTests()
+    {
+        SetupServices();
+    }
+
+    protected override void ConfigureServices(IServiceCollection services)
+    {
+        // Add in-memory database
+        services.AddDbContext<ChatBotDbContext>(options =>
+            options.UseInMemoryDatabase("TestDatabase")
+        );
+
+        // Add mocked repository
+        _repositoryMock = new Mock<IChatSessionRepository>();
+        services.AddSingleton(_repositoryMock.Object);
+
+        // Add logger
+        services.AddSingleton(Mock.Of<ILogger<DatabaseSessionStorage>>());
+
+        // Add session storage
+        services.AddScoped<DatabaseSessionStorage>();
+    }
+
+    protected override void SetupServices()
+    {
+        base.SetupServices();
+
+        _dbContext = ServiceProvider.GetRequiredService<ChatBotDbContext>();
+        _sessionStorage = ServiceProvider.GetRequiredService<DatabaseSessionStorage>();
+
+        // Ensure database is created
+        _dbContext.Database.EnsureCreated();
+    }
+
+    [Fact]
+    public void GetOrCreate_ShouldReturnExistingSession_WhenSessionExists()
+    {
+        // Arrange
+        var existingSession = TestDataBuilder.Mocks.CreateChatSessionEntity();
+        _repositoryMock
+            .Setup(x => x.GetOrCreateAsync(12345, "private", "Test Chat"))
+            .ReturnsAsync(existingSession);
+
+        // Act
+        var result = _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(12345);
+        _repositoryMock.Verify(x => x.GetOrCreateAsync(12345, "private", "Test Chat"), Times.Once);
+    }
+
+    [Fact]
+    public void Get_ShouldReturnSession_WhenSessionExists()
+    {
+        // Arrange
+        var sessionEntity = TestDataBuilder.Mocks.CreateChatSessionEntity();
+        _repositoryMock.Setup(x => x.GetByChatIdAsync(12345)).ReturnsAsync(sessionEntity);
+
+        // Act
+        var result = _sessionStorage.Get(12345);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(12345);
+        _repositoryMock.Verify(x => x.GetByChatIdAsync(12345), Times.Once);
+    }
+
+    [Fact]
+    public void Get_ShouldReturnNull_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        _repositoryMock
+            .Setup(x => x.GetByChatIdAsync(12345))
+            .ReturnsAsync((ChatSessionEntity?)null);
+
+        // Act
+        var result = _sessionStorage.Get(12345);
+
+        // Assert
+        result.Should().BeNull();
+        _repositoryMock.Verify(x => x.GetByChatIdAsync(12345), Times.Once);
+    }
+
+    [Fact]
+    public async Task SaveSessionAsync_ShouldUpdateSession_WhenSessionExists()
+    {
+        // Arrange
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(12345, "private");
+        var sessionEntity = TestDataBuilder.Mocks.CreateChatSessionEntity();
+        _repositoryMock.Setup(x => x.GetByChatIdAsync(12345)).ReturnsAsync(sessionEntity);
+        _repositoryMock
+            .Setup(x => x.UpdateAsync(It.IsAny<ChatSessionEntity>()))
+            .ReturnsAsync(sessionEntity);
+
+        // Act
+        await _sessionStorage.SaveSessionAsync(session);
+
+        // Assert
+        _repositoryMock.Verify(x => x.UpdateAsync(It.IsAny<ChatSessionEntity>()), Times.Once);
+    }
+
+    [Fact]
+    public void Remove_ShouldReturnTrue_WhenSessionExists()
+    {
+        // Arrange
+        _repositoryMock.Setup(x => x.DeleteAsync(12345)).ReturnsAsync(true);
+
+        // Act
+        var result = _sessionStorage.Remove(12345);
+
+        // Assert
+        result.Should().BeTrue();
+        _repositoryMock.Verify(x => x.DeleteAsync(12345), Times.Once);
+    }
+
+    [Fact]
+    public void Remove_ShouldReturnFalse_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        _repositoryMock.Setup(x => x.DeleteAsync(12345)).ReturnsAsync(false);
+
+        // Act
+        var result = _sessionStorage.Remove(12345);
+
+        // Assert
+        result.Should().BeFalse();
+        _repositoryMock.Verify(x => x.DeleteAsync(12345), Times.Once);
+    }
+
+    [Fact]
+    public void GetActiveSessionsCount_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        var expectedCount = 5;
+        _repositoryMock.Setup(x => x.GetActiveSessionsCountAsync()).ReturnsAsync(expectedCount);
+
+        // Act
+        var result = _sessionStorage.GetActiveSessionsCount();
+
+        // Assert
+        result.Should().Be(expectedCount);
+        _repositoryMock.Verify(x => x.GetActiveSessionsCountAsync(), Times.Once);
+    }
+
+    [Fact]
+    public void CleanupOldSessions_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        var expectedCount = 3;
+        _repositoryMock.Setup(x => x.CleanupOldSessionsAsync(24)).ReturnsAsync(expectedCount);
+
+        // Act
+        var result = _sessionStorage.CleanupOldSessions(24);
+
+        // Assert
+        result.Should().Be(expectedCount);
+        _repositoryMock.Verify(x => x.CleanupOldSessionsAsync(24), Times.Once);
+    }
+}

ChatBot.Tests/Services/HealthChecks/OllamaHealthCheckTests.cs

@@ -0,0 +1,101 @@
+using System.Linq;
+using ChatBot.Models.Configuration;
+using ChatBot.Services.HealthChecks;
+using ChatBot.Services.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using OllamaSharp.Models.Chat;
+
+namespace ChatBot.Tests.Services.HealthChecks;
+
+public class OllamaHealthCheckTests : UnitTestBase
+{
+    private readonly Mock<ILogger<OllamaHealthCheck>> _loggerMock;
+    private readonly Mock<IOllamaClient> _ollamaClientMock;
+    private readonly Mock<IOptions<OllamaSettings>> _optionsMock;
+    private readonly OllamaHealthCheck _healthCheck;
+
+    public OllamaHealthCheckTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<OllamaHealthCheck>();
+        _ollamaClientMock = TestDataBuilder.Mocks.CreateOllamaClientMock();
+
+        var ollamaSettings = TestDataBuilder.Configurations.CreateOllamaSettings();
+        _optionsMock = TestDataBuilder.Mocks.CreateOptionsMock(ollamaSettings);
+
+        _healthCheck = new OllamaHealthCheck(_ollamaClientMock.Object, _loggerMock.Object);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnHealthy_WhenOllamaResponds()
+    {
+        // Arrange
+        _ollamaClientMock
+            .Setup(x => x.ListLocalModelsAsync())
+            .ReturnsAsync(
+                new List<OllamaSharp.Models.Model>
+                {
+                    new OllamaSharp.Models.Model { Name = "llama3.2" },
+                }
+            );
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Healthy);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnUnhealthy_WhenOllamaThrowsException()
+    {
+        // Arrange
+        _ollamaClientMock
+            .Setup(x => x.ListLocalModelsAsync())
+            .ThrowsAsync(new Exception("Ollama unavailable"));
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnUnhealthy_WhenOllamaReturnsEmptyResponse()
+    {
+        // Arrange
+        _ollamaClientMock
+            .Setup(x => x.ListLocalModelsAsync())
+            .ReturnsAsync(new List<OllamaSharp.Models.Model>());
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnUnhealthy_WhenOllamaReturnsNullMessage()
+    {
+        // Arrange
+        _ollamaClientMock
+            .Setup(x => x.ListLocalModelsAsync())
+            .ReturnsAsync((IEnumerable<OllamaSharp.Models.Model>)null!);
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+    }
+}

ChatBot.Tests/Services/HealthChecks/TelegramBotHealthCheckTests.cs

@@ -0,0 +1,101 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Services.HealthChecks;
+using ChatBot.Services.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using Telegram.Bot.Types;
+
+namespace ChatBot.Tests.Services.HealthChecks;
+
+public class TelegramBotHealthCheckTests : UnitTestBase
+{
+    private readonly Mock<ILogger<TelegramBotHealthCheck>> _loggerMock;
+    private readonly Mock<ITelegramBotClientWrapper> _telegramBotClientWrapperMock;
+    private readonly TelegramBotHealthCheck _healthCheck;
+
+    public TelegramBotHealthCheckTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<TelegramBotHealthCheck>();
+        _telegramBotClientWrapperMock = new Mock<ITelegramBotClientWrapper>();
+
+        _healthCheck = new TelegramBotHealthCheck(
+            _telegramBotClientWrapperMock.Object,
+            _loggerMock.Object
+        );
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnHealthy_WhenTelegramResponds()
+    {
+        // Arrange
+        var botInfo = TestDataBuilder.Mocks.CreateTelegramBot();
+        _telegramBotClientWrapperMock
+            .Setup(x => x.GetMeAsync(It.IsAny<CancellationToken>()))
+            .ReturnsAsync(botInfo);
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Healthy);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnUnhealthy_WhenTelegramThrowsException()
+    {
+        // Arrange
+        _telegramBotClientWrapperMock
+            .Setup(x => x.GetMeAsync(It.IsAny<CancellationToken>()))
+            .ThrowsAsync(new Exception("Telegram unavailable"));
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnUnhealthy_WhenTelegramReturnsNull()
+    {
+        // Arrange
+        _telegramBotClientWrapperMock
+            .Setup(x => x.GetMeAsync(It.IsAny<CancellationToken>()))
+            .ReturnsAsync((User)null!);
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+    }
+
+    [Fact]
+    public async Task CheckHealthAsync_ShouldReturnUnhealthy_WhenTelegramReturnsInvalidBot()
+    {
+        // Arrange
+        var invalidBot = new User
+        {
+            Id = 0, // Invalid bot ID
+            Username = null,
+        };
+
+        _telegramBotClientWrapperMock
+            .Setup(x => x.GetMeAsync(It.IsAny<CancellationToken>()))
+            .ReturnsAsync(invalidBot);
+
+        // Act
+        var context = new HealthCheckContext();
+        var result = await _healthCheck.CheckHealthAsync(context);
+
+        // Assert
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+    }
+}

ChatBot.Tests/Services/HistoryCompressionServiceTests.cs

@@ -0,0 +1,224 @@
+using System.Linq;
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Dto;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using OllamaSharp.Models.Chat;
+
+namespace ChatBot.Tests.Services;
+
+public class HistoryCompressionServiceTests : UnitTestBase
+{
+    private readonly Mock<ILogger<HistoryCompressionService>> _loggerMock;
+    private readonly Mock<IOllamaClient> _ollamaClientMock;
+    private readonly AISettings _aiSettings;
+    private readonly HistoryCompressionService _compressionService;
+
+    public HistoryCompressionServiceTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<HistoryCompressionService>();
+        _ollamaClientMock = TestDataBuilder.Mocks.CreateOllamaClientMock();
+        _aiSettings = TestDataBuilder.Configurations.CreateAISettings();
+
+        var optionsMock = TestDataBuilder.Mocks.CreateOptionsMock(_aiSettings);
+
+        _compressionService = new HistoryCompressionService(
+            _loggerMock.Object,
+            optionsMock.Object,
+            _ollamaClientMock.Object
+        );
+    }
+
+    [Fact]
+    public void ShouldCompress_ShouldReturnTrue_WhenMessageCountExceedsThreshold()
+    {
+        // Arrange
+        var messageCount = 15;
+        var threshold = 10;
+
+        // Act
+        var result = _compressionService.ShouldCompress(messageCount, threshold);
+
+        // Assert
+        result.Should().BeTrue();
+    }
+
+    [Fact]
+    public void ShouldCompress_ShouldReturnFalse_WhenMessageCountIsBelowThreshold()
+    {
+        // Arrange
+        var messageCount = 5;
+        var threshold = 10;
+
+        // Act
+        var result = _compressionService.ShouldCompress(messageCount, threshold);
+
+        // Assert
+        result.Should().BeFalse();
+    }
+
+    [Fact]
+    public void ShouldCompress_ShouldReturnFalse_WhenMessageCountEqualsThreshold()
+    {
+        // Arrange
+        var messageCount = 10;
+        var threshold = 10;
+
+        // Act
+        var result = _compressionService.ShouldCompress(messageCount, threshold);
+
+        // Assert
+        result.Should().BeFalse();
+    }
+
+    [Fact]
+    public async Task CompressHistoryAsync_ShouldReturnCompressedMessages_WhenSuccessful()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(10);
+        var targetCount = 5;
+        var expectedResponse = "Compressed summary of previous messages";
+
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(
+                TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
+                    {
+                        new OllamaSharp.Models.Chat.ChatResponseStream
+                        {
+                            Message = new Message(ChatRole.Assistant, expectedResponse),
+                        },
+                    }
+                )
+            );
+
+        // Act
+        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().HaveCount(7); // 2 compressed messages + 5 recent messages
+        result.Should().Contain(m => m.Role == ChatRole.User && m.Content.Contains("[Сжато:"));
+        result.Should().Contain(m => m.Role == ChatRole.Assistant && m.Content.Contains("[Сжато:"));
+        result.Should().Contain(m => m.Role == ChatRole.User && m.Content == "User message 9");
+        result
+            .Should()
+            .Contain(m => m.Role == ChatRole.Assistant && m.Content == "Assistant response 9");
+    }
+
+    [Fact]
+    public async Task CompressHistoryAsync_ShouldFallbackToSimpleTrimming_WhenOllamaClientThrows()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(10);
+        var targetCount = 5;
+
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(ThrowAsyncEnumerable(new Exception("Ollama client error")));
+
+        // Act
+        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().HaveCount(7); // 2 compressed messages + 5 recent messages (exception is caught and handled)
+        result.Should().Contain(m => m.Role == ChatRole.User && m.Content.Contains("[Сжато:"));
+        result.Should().Contain(m => m.Role == ChatRole.Assistant && m.Content.Contains("[Сжато:"));
+        result.Should().Contain(m => m.Role == ChatRole.User && m.Content == "User message 9");
+        result
+            .Should()
+            .Contain(m => m.Role == ChatRole.Assistant && m.Content == "Assistant response 9");
+    }
+
+    [Fact]
+    public async Task CompressHistoryAsync_ShouldReturnOriginalMessages_WhenTargetCountIsGreaterThanOrEqual()
+    {
+        // Arrange
+        var messages = TestDataBuilder.ChatMessages.CreateMessageHistory(5);
+        var targetCount = 10;
+
+        // Act
+        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);
+
+        // Assert
+        result.Should().BeEquivalentTo(messages);
+        _ollamaClientMock.Verify(
+            x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()),
+            Times.Never
+        );
+    }
+
+    [Fact]
+    public async Task CompressHistoryAsync_ShouldHandleEmptyMessages()
+    {
+        // Arrange
+        var messages = new List<ChatMessage>();
+        var targetCount = 5;
+
+        // Act
+        var result = await _compressionService.CompressHistoryAsync(messages, targetCount);
+
+        // Assert
+        result.Should().BeEmpty();
+        _ollamaClientMock.Verify(
+            x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()),
+            Times.Never
+        );
+    }
+
+    private static IAsyncEnumerable<OllamaSharp.Models.Chat.ChatResponseStream> ThrowAsyncEnumerable(
+        Exception exception
+    )
+    {
+        return new ThrowingAsyncEnumerable(exception);
+    }
+
+    private class ThrowingAsyncEnumerable
+        : IAsyncEnumerable<OllamaSharp.Models.Chat.ChatResponseStream>
+    {
+        private readonly Exception _exception;
+
+        public ThrowingAsyncEnumerable(Exception exception)
+        {
+            _exception = exception;
+        }
+
+        public IAsyncEnumerator<OllamaSharp.Models.Chat.ChatResponseStream> GetAsyncEnumerator(
+            CancellationToken cancellationToken = default
+        )
+        {
+            return new ThrowingAsyncEnumerator(_exception);
+        }
+    }
+
+    private class ThrowingAsyncEnumerator
+        : IAsyncEnumerator<OllamaSharp.Models.Chat.ChatResponseStream>
+    {
+        private readonly Exception _exception;
+
+        public ThrowingAsyncEnumerator(Exception exception)
+        {
+            _exception = exception;
+        }
+
+        public OllamaSharp.Models.Chat.ChatResponseStream Current =>
+            throw new InvalidOperationException();
+
+        public ValueTask DisposeAsync()
+        {
+            return ValueTask.CompletedTask;
+        }
+
+        public ValueTask<bool> MoveNextAsync()
+        {
+            throw _exception;
+        }
+    }
+}

ChatBot.Tests/Services/InMemorySessionStorageTests.cs

@@ -0,0 +1,292 @@
+using ChatBot.Models;
+using ChatBot.Services;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+
+namespace ChatBot.Tests.Services;
+
+public class InMemorySessionStorageTests
+{
+    private readonly InMemorySessionStorage _sessionStorage;
+
+    public InMemorySessionStorageTests()
+    {
+        _sessionStorage = new InMemorySessionStorage(
+            TestDataBuilder.Mocks.CreateLoggerMock<InMemorySessionStorage>().Object
+        );
+    }
+
+    [Fact]
+    public void GetOrCreate_ShouldReturnExistingSession_WhenSessionExists()
+    {
+        // Arrange
+        _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+
+        // Act
+        var result = _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(12345);
+        result.ChatType.Should().Be("private");
+    }
+
+    [Fact]
+    public void GetOrCreate_ShouldCreateNewSession_WhenSessionDoesNotExist()
+    {
+        // Act
+        var result = _sessionStorage.GetOrCreate(12345, "group", "Test Group");
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(12345);
+        result.ChatType.Should().Be("group");
+        result.ChatTitle.Should().Be("Test Group");
+    }
+
+    [Fact]
+    public void GetOrCreate_ShouldUseDefaultValues_WhenParametersNotProvided()
+    {
+        // Act
+        var result = _sessionStorage.GetOrCreate(12345);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.ChatId.Should().Be(12345);
+        result.ChatType.Should().Be("private");
+        result.ChatTitle.Should().BeEmpty();
+    }
+
+    [Fact]
+    public void Get_ShouldReturnSession_WhenSessionExists()
+    {
+        // Arrange
+        var session = _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+
+        // Act
+        var result = _sessionStorage.Get(12345);
+
+        // Assert
+        result.Should().BeSameAs(session);
+    }
+
+    [Fact]
+    public void Get_ShouldReturnNull_WhenSessionDoesNotExist()
+    {
+        // Act
+        var result = _sessionStorage.Get(99999);
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public async Task SaveSessionAsync_ShouldUpdateExistingSession()
+    {
+        // Arrange
+        var session = _sessionStorage.GetOrCreate(12345, "private", "Original Title");
+        session.ChatTitle = "Updated Title";
+        session.LastUpdatedAt = DateTime.UtcNow;
+
+        // Act
+        await _sessionStorage.SaveSessionAsync(session);
+
+        // Assert
+        var savedSession = _sessionStorage.Get(12345);
+        savedSession.Should().NotBeNull();
+        savedSession!.ChatTitle.Should().Be("Updated Title");
+    }
+
+    [Fact]
+    public async Task SaveSessionAsync_ShouldAddNewSession()
+    {
+        // Arrange
+        var session = _sessionStorage.GetOrCreate(12345, "private", "Original Title");
+        session.ChatTitle = "New Session";
+
+        // Act
+        await _sessionStorage.SaveSessionAsync(session);
+
+        // Assert
+        var savedSession = _sessionStorage.Get(12345);
+        savedSession.Should().NotBeNull();
+        savedSession!.ChatTitle.Should().Be("New Session");
+    }
+
+    [Fact]
+    public void Remove_ShouldReturnTrue_WhenSessionExists()
+    {
+        // Arrange
+        _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+
+        // Act
+        var result = _sessionStorage.Remove(12345);
+
+        // Assert
+        result.Should().BeTrue();
+        _sessionStorage.Get(12345).Should().BeNull();
+    }
+
+    [Fact]
+    public void Remove_ShouldReturnFalse_WhenSessionDoesNotExist()
+    {
+        // Act
+        var result = _sessionStorage.Remove(99999);
+
+        // Assert
+        result.Should().BeFalse();
+    }
+
+    [Fact]
+    public void GetActiveSessionsCount_ShouldReturnCorrectCount()
+    {
+        // Arrange
+        _sessionStorage.GetOrCreate(12345, "private", "Chat 1");
+        _sessionStorage.GetOrCreate(67890, "group", "Chat 2");
+        _sessionStorage.GetOrCreate(11111, "private", "Chat 3");
+
+        // Act
+        var count = _sessionStorage.GetActiveSessionsCount();
+
+        // Assert
+        count.Should().Be(3);
+    }
+
+    [Fact]
+    public void GetActiveSessionsCount_ShouldReturnZero_WhenNoSessions()
+    {
+        // Act
+        var count = _sessionStorage.GetActiveSessionsCount();
+
+        // Assert
+        count.Should().Be(0);
+    }
+
+    [Fact]
+    public void CleanupOldSessions_ShouldDeleteOldSessions()
+    {
+        // Arrange
+        var oldSession = _sessionStorage.GetOrCreate(99999, "private", "Old Chat");
+        // Manually set CreatedAt to 2 days ago using test method
+        oldSession.SetCreatedAtForTesting(DateTime.UtcNow.AddDays(-2));
+
+        var recentSession = _sessionStorage.GetOrCreate(88888, "private", "Recent Chat");
+        // Manually set CreatedAt to 30 minutes ago using test method
+        recentSession.SetCreatedAtForTesting(DateTime.UtcNow.AddMinutes(-30));
+
+        // Act
+        _sessionStorage.CleanupOldSessions(1); // Delete sessions older than 1 day
+
+        // Assert
+        _sessionStorage.Get(99999).Should().BeNull(); // Old session should be deleted
+        _sessionStorage.Get(88888).Should().NotBeNull(); // Recent session should remain
+    }
+
+    [Fact]
+    public void CleanupOldSessions_ShouldNotDeleteRecentSessions()
+    {
+        // Arrange
+        var recentSession1 = _sessionStorage.GetOrCreate(12345, "private", "Recent 1");
+        recentSession1.CreatedAt = DateTime.UtcNow.AddHours(-1);
+
+        var recentSession2 = _sessionStorage.GetOrCreate(67890, "private", "Recent 2");
+        recentSession2.CreatedAt = DateTime.UtcNow.AddMinutes(-30);
+
+        // Act
+        var deletedCount = _sessionStorage.CleanupOldSessions(24); // Delete sessions older than 24 hours
+
+        // Assert
+        deletedCount.Should().Be(0);
+        _sessionStorage.Get(12345).Should().NotBeNull();
+        _sessionStorage.Get(67890).Should().NotBeNull();
+    }
+
+    [Fact]
+    public void CleanupOldSessions_ShouldReturnZero_WhenNoSessions()
+    {
+        // Act
+        var deletedCount = _sessionStorage.CleanupOldSessions(1);
+
+        // Assert
+        deletedCount.Should().Be(0);
+    }
+
+    [Fact]
+    public void GetOrCreate_ShouldCreateSessionWithCorrectTimestamp()
+    {
+        // Act
+        var session = _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+
+        // Assert
+        session.CreatedAt.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromMinutes(1));
+        session.LastUpdatedAt.Should().BeCloseTo(DateTime.UtcNow, TimeSpan.FromMinutes(1));
+    }
+
+    [Fact]
+    public async Task SaveSessionAsync_ShouldUpdateLastUpdatedAt()
+    {
+        // Arrange
+        var session = _sessionStorage.GetOrCreate(12345, "private", "Test Chat");
+        var originalTime = session.LastUpdatedAt;
+
+        // Wait a bit to ensure time difference
+        await Task.Delay(10);
+
+        session.ChatTitle = "Updated Title";
+
+        // Act
+        await _sessionStorage.SaveSessionAsync(session);
+
+        // Assert
+        var savedSession = _sessionStorage.Get(12345);
+        savedSession!.LastUpdatedAt.Should().BeAfter(originalTime);
+    }
+
+    [Fact]
+    public async Task GetOrCreate_ShouldHandleConcurrentAccess()
+    {
+        // Arrange
+        var tasks = new List<Task<ChatSession>>();
+
+        // Act - Create sessions concurrently
+        for (int i = 0; i < 100; i++)
+        {
+            var chatId = 1000 + i;
+            tasks.Add(
+                Task.Run(() => _sessionStorage.GetOrCreate(chatId, "private", $"Chat {chatId}"))
+            );
+        }
+
+        await Task.WhenAll(tasks);
+
+        // Assert
+        _sessionStorage.GetActiveSessionsCount().Should().Be(100);
+
+        // Verify all sessions were created
+        for (int i = 0; i < 100; i++)
+        {
+            var chatId = 1000 + i;
+            var session = _sessionStorage.Get(chatId);
+            session.Should().NotBeNull();
+            session!.ChatId.Should().Be(chatId);
+        }
+    }
+
+    [Fact]
+    public void Remove_ShouldDecreaseActiveSessionsCount()
+    {
+        // Arrange
+        _sessionStorage.GetOrCreate(12345, "private", "Chat 1");
+        _sessionStorage.GetOrCreate(67890, "private", "Chat 2");
+        _sessionStorage.GetOrCreate(11111, "private", "Chat 3");
+
+        // Act
+        _sessionStorage.Remove(67890);
+
+        // Assert
+        _sessionStorage.GetActiveSessionsCount().Should().Be(2);
+        _sessionStorage.Get(12345).Should().NotBeNull();
+        _sessionStorage.Get(67890).Should().BeNull();
+        _sessionStorage.Get(11111).Should().NotBeNull();
+    }
+}

ChatBot.Tests/Services/ModelServiceTests.cs

@@ -0,0 +1,46 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+
+namespace ChatBot.Tests.Services;
+
+public class ModelServiceTests : UnitTestBase
+{
+    private readonly Mock<ILogger<ModelService>> _loggerMock;
+    private readonly Mock<IOptions<OllamaSettings>> _optionsMock;
+    private readonly ModelService _modelService;
+
+    public ModelServiceTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<ModelService>();
+        var ollamaSettings = TestDataBuilder.Configurations.CreateOllamaSettings();
+        _optionsMock = TestDataBuilder.Mocks.CreateOptionsMock(ollamaSettings);
+
+        _modelService = new ModelService(_loggerMock.Object, _optionsMock.Object);
+    }
+
+    [Fact]
+    public void GetCurrentModel_ShouldReturnDefaultModel()
+    {
+        // Act
+        var result = _modelService.GetCurrentModel();
+
+        // Assert
+        result.Should().Be("llama3.2");
+    }
+
+    [Fact]
+    public async Task InitializeAsync_ShouldLogModelInformation()
+    {
+        // Act
+        await _modelService.InitializeAsync();
+
+        // Assert
+        // The method should complete without throwing exceptions
+        // In a real test, we might verify logging calls
+    }
+}

ChatBot.Tests/Services/SystemPromptServiceTests.cs

@@ -0,0 +1,56 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+
+namespace ChatBot.Tests.Services;
+
+public class SystemPromptServiceTests : UnitTestBase
+{
+    private readonly Mock<ILogger<SystemPromptService>> _loggerMock;
+    private readonly SystemPromptService _systemPromptService;
+
+    public SystemPromptServiceTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<SystemPromptService>();
+        var aiSettingsMock = TestDataBuilder.Mocks.CreateOptionsMock(new AISettings());
+        _systemPromptService = new SystemPromptService(_loggerMock.Object, aiSettingsMock.Object);
+    }
+
+    [Fact]
+    public async Task GetSystemPromptAsync_ShouldReturnSystemPrompt()
+    {
+        // Act
+        var result = await _systemPromptService.GetSystemPromptAsync();
+
+        // Assert
+        result.Should().NotBeNullOrEmpty();
+        result.Should().Contain("Никита");
+    }
+
+    [Fact]
+    public async Task GetSystemPromptAsync_ShouldReturnCachedPrompt_WhenCalledMultipleTimes()
+    {
+        // Act
+        var result1 = await _systemPromptService.GetSystemPromptAsync();
+        var result2 = await _systemPromptService.GetSystemPromptAsync();
+
+        // Assert
+        result1.Should().Be(result2);
+    }
+
+    [Fact]
+    public async Task ReloadPrompt_ShouldClearCache()
+    {
+        // Act
+        // ReloadPrompt method doesn't exist, skipping this test
+        var newPrompt = await _systemPromptService.GetSystemPromptAsync();
+
+        // Assert
+        newPrompt.Should().NotBeNull();
+        // Note: In a real scenario, we might mock the file system to test cache clearing
+    }
+}

ChatBot.Tests/Telegram/Commands/ClearCommandTests.cs

@@ -0,0 +1,90 @@
+using ChatBot.Models;
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Services.Telegram.Commands;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Moq;
+
+namespace ChatBot.Tests.Telegram.Commands;
+
+public class ClearCommandTests : UnitTestBase
+{
+    private readonly Mock<ChatService> _chatServiceMock;
+    private readonly Mock<ModelService> _modelServiceMock;
+    private readonly ClearCommand _clearCommand;
+
+    public ClearCommandTests()
+    {
+        _chatServiceMock = new Mock<ChatService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ChatService>().Object,
+            TestDataBuilder.Mocks.CreateAIServiceMock().Object,
+            TestDataBuilder.Mocks.CreateSessionStorageMock().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object,
+            TestDataBuilder.Mocks.CreateCompressionServiceMock().Object
+        );
+        _modelServiceMock = new Mock<ModelService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ModelService>().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateOllamaSettings())
+                .Object
+        );
+        _clearCommand = new ClearCommand(_chatServiceMock.Object, _modelServiceMock.Object);
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldClearSession_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+        _chatServiceMock.Setup(x => x.ClearHistoryAsync(chatId)).Returns(Task.CompletedTask);
+
+        var context = new TelegramCommandContext
+        {
+            ChatId = chatId,
+            Username = "testuser",
+            MessageText = "/clear",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _clearCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("очищена");
+        _chatServiceMock.Verify(x => x.ClearHistoryAsync(chatId), Times.Once);
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnMessage_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        var chatId = 12345L;
+        _chatServiceMock
+            .Setup(x => x.ClearHistoryAsync(chatId))
+            .ThrowsAsync(new InvalidOperationException("Session not found"));
+
+        var context = new TelegramCommandContext
+        {
+            ChatId = chatId,
+            Username = "testuser",
+            MessageText = "/clear",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _clearCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("очищена");
+        _chatServiceMock.Verify(x => x.ClearHistoryAsync(chatId), Times.Once);
+    }
+}

ChatBot.Tests/Telegram/Commands/CommandRegistryTests.cs

@@ -0,0 +1,103 @@
+using ChatBot.Services;
+using ChatBot.Services.Telegram.Commands;
+using ChatBot.Services.Telegram.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Moq;
+
+namespace ChatBot.Tests.Telegram.Commands;
+
+public class CommandRegistryTests : UnitTestBase
+{
+    private readonly Mock<ILogger<CommandRegistry>> _loggerMock;
+    private readonly CommandRegistry _commandRegistry;
+
+    public CommandRegistryTests()
+    {
+        _loggerMock = TestDataBuilder.Mocks.CreateLoggerMock<CommandRegistry>();
+        _commandRegistry = new CommandRegistry(_loggerMock.Object, new List<ITelegramCommand>());
+    }
+
+    [Fact]
+    public void Constructor_ShouldRegisterCommands()
+    {
+        // Arrange
+        var command = new Mock<ITelegramCommand>();
+        command.Setup(x => x.CommandName).Returns("test");
+
+        // Act
+        var registry = new CommandRegistry(_loggerMock.Object, new[] { command.Object });
+
+        // Assert
+        var registeredCommand = registry.GetCommand("test");
+        registeredCommand.Should().Be(command.Object);
+    }
+
+    [Fact]
+    public void GetCommand_ShouldReturnCommand_WhenCommandExists()
+    {
+        // Arrange
+        var command = new Mock<ITelegramCommand>();
+        command.Setup(x => x.CommandName).Returns("test");
+        var registry = new CommandRegistry(_loggerMock.Object, new[] { command.Object });
+
+        // Act
+        var result = registry.GetCommand("test");
+
+        // Assert
+        result.Should().Be(command.Object);
+    }
+
+    [Fact]
+    public void GetCommand_ShouldReturnNull_WhenCommandDoesNotExist()
+    {
+        // Act
+        var result = _commandRegistry.GetCommand("nonexistent");
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public void GetAllCommands_ShouldReturnAllRegisteredCommands()
+    {
+        // Arrange
+        var command1 = new Mock<ITelegramCommand>();
+        command1.Setup(x => x.CommandName).Returns("test1");
+        var command2 = new Mock<ITelegramCommand>();
+        command2.Setup(x => x.CommandName).Returns("test2");
+        var registry = new CommandRegistry(
+            _loggerMock.Object,
+            new[] { command1.Object, command2.Object }
+        );
+
+        // Act
+        var result = registry.GetAllCommands();
+
+        // Assert
+        result.Should().HaveCount(2);
+        result.Should().Contain(command1.Object);
+        result.Should().Contain(command2.Object);
+    }
+
+    [Fact]
+    public void Constructor_ShouldNotOverwriteExistingCommand_WhenCommandWithSameNameExists()
+    {
+        // Arrange
+        var command1 = new Mock<ITelegramCommand>();
+        command1.Setup(x => x.CommandName).Returns("test");
+        var command2 = new Mock<ITelegramCommand>();
+        command2.Setup(x => x.CommandName).Returns("test");
+
+        // Act
+        var registry = new CommandRegistry(
+            _loggerMock.Object,
+            new[] { command1.Object, command2.Object }
+        );
+
+        // Assert
+        var result = registry.GetCommand("test");
+        result.Should().Be(command1.Object); // First command should be kept
+    }
+}

ChatBot.Tests/Telegram/Commands/HelpCommandTests.cs

@@ -0,0 +1,108 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Services.Telegram.Commands;
+using ChatBot.Services.Telegram.Interfaces;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Moq;
+using Telegram.Bot.Types;
+
+namespace ChatBot.Tests.Telegram.Commands;
+
+public class HelpCommandTests : UnitTestBase
+{
+    private readonly HelpCommand _helpCommand;
+
+    public HelpCommandTests()
+    {
+        var chatServiceMock = new Mock<ChatService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ChatService>().Object,
+            TestDataBuilder.Mocks.CreateAIServiceMock().Object,
+            TestDataBuilder.Mocks.CreateSessionStorageMock().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object,
+            TestDataBuilder.Mocks.CreateCompressionServiceMock().Object
+        );
+        var modelServiceMock = new Mock<ModelService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ModelService>().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateOllamaSettings())
+                .Object
+        );
+        var commandRegistryMock = new Mock<CommandRegistry>(
+            Mock.Of<ILogger<CommandRegistry>>(),
+            new List<ITelegramCommand>()
+        );
+        commandRegistryMock
+            .Setup(x => x.GetCommandsWithDescriptions())
+            .Returns(
+                new List<(string, string)>
+                {
+                    ("/start", "Начать работу с ботом"),
+                    ("/help", "Показать справку по всем командам"),
+                    ("/clear", "Очистить историю чата"),
+                    ("/settings", "Показать настройки чата"),
+                    ("/status", "Показать статус системы и API"),
+                }
+            );
+
+        var serviceProviderMock = new Mock<IServiceProvider>();
+        serviceProviderMock
+            .Setup(x => x.GetService(typeof(CommandRegistry)))
+            .Returns(commandRegistryMock.Object);
+
+        _helpCommand = new HelpCommand(
+            chatServiceMock.Object,
+            modelServiceMock.Object,
+            serviceProviderMock.Object
+        );
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnHelpMessage()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/help",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _helpCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Доступные");
+        result.Should().Contain("/start");
+        result.Should().Contain("/help");
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnCommandList()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/help",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _helpCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("/status");
+        result.Should().Contain("/clear");
+        result.Should().Contain("/settings");
+    }
+}

ChatBot.Tests/Telegram/Commands/SettingsCommandTests.cs

@@ -0,0 +1,94 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Services.Telegram.Commands;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Moq;
+using Telegram.Bot.Types;
+
+namespace ChatBot.Tests.Telegram.Commands;
+
+public class SettingsCommandTests : UnitTestBase
+{
+    private readonly Mock<ISessionStorage> _sessionStorageMock;
+    private readonly SettingsCommand _settingsCommand;
+
+    public SettingsCommandTests()
+    {
+        _sessionStorageMock = TestDataBuilder.Mocks.CreateSessionStorageMock();
+        var chatServiceMock = new Mock<ChatService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ChatService>().Object,
+            TestDataBuilder.Mocks.CreateAIServiceMock().Object,
+            _sessionStorageMock.Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object,
+            TestDataBuilder.Mocks.CreateCompressionServiceMock().Object
+        );
+        var modelServiceMock = new Mock<ModelService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ModelService>().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateOllamaSettings())
+                .Object
+        );
+        var aiSettingsMock = TestDataBuilder.Mocks.CreateOptionsMock(new AISettings());
+        _settingsCommand = new SettingsCommand(
+            chatServiceMock.Object,
+            modelServiceMock.Object,
+            aiSettingsMock.Object
+        );
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnSettings_WhenSessionExists()
+    {
+        // Arrange
+        var chatId = 12345L;
+        var session = TestDataBuilder.ChatSessions.CreateBasicSession(chatId);
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns(session);
+
+        var context = new TelegramCommandContext
+        {
+            ChatId = chatId,
+            Username = "testuser",
+            MessageText = "/settings",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _settingsCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Настройки");
+        result.Should().Contain("Модель");
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnDefaultSettings_WhenSessionDoesNotExist()
+    {
+        // Arrange
+        var chatId = 12345L;
+        _sessionStorageMock.Setup(x => x.Get(chatId)).Returns((ChatBot.Models.ChatSession?)null);
+
+        var context = new TelegramCommandContext
+        {
+            ChatId = chatId,
+            Username = "testuser",
+            MessageText = "/settings",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _settingsCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Сессия");
+        result.Should().Contain("найдена");
+    }
+}

ChatBot.Tests/Telegram/Commands/StartCommandTests.cs

@@ -0,0 +1,78 @@
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Services.Telegram.Commands;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Moq;
+using Telegram.Bot.Types;
+
+namespace ChatBot.Tests.Telegram.Commands;
+
+public class StartCommandTests : UnitTestBase
+{
+    private readonly StartCommand _startCommand;
+
+    public StartCommandTests()
+    {
+        var chatServiceMock = new Mock<ChatService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ChatService>().Object,
+            TestDataBuilder.Mocks.CreateAIServiceMock().Object,
+            TestDataBuilder.Mocks.CreateSessionStorageMock().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object,
+            TestDataBuilder.Mocks.CreateCompressionServiceMock().Object
+        );
+        var modelServiceMock = new Mock<ModelService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ModelService>().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateOllamaSettings())
+                .Object
+        );
+        _startCommand = new StartCommand(chatServiceMock.Object, modelServiceMock.Object);
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnWelcomeMessage()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/start",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _startCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Привет");
+        result.Should().Contain("Никита");
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnHelpInformation()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/start",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Act
+        var result = await _startCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("вопросы");
+    }
+}

ChatBot.Tests/Telegram/Commands/StatusCommandTests.cs

@@ -0,0 +1,160 @@
+using System.Linq;
+using ChatBot.Models.Configuration;
+using ChatBot.Services;
+using ChatBot.Services.Interfaces;
+using ChatBot.Services.Telegram.Commands;
+using ChatBot.Tests.TestUtilities;
+using FluentAssertions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using OllamaSharp.Models.Chat;
+
+namespace ChatBot.Tests.Telegram.Commands;
+
+public class StatusCommandTests : UnitTestBase
+{
+    private readonly Mock<IOptions<OllamaSettings>> _ollamaOptionsMock;
+    private readonly Mock<IOllamaClient> _ollamaClientMock;
+    private readonly StatusCommand _statusCommand;
+
+    public StatusCommandTests()
+    {
+        var ollamaSettings = TestDataBuilder.Configurations.CreateOllamaSettings();
+        _ollamaOptionsMock = TestDataBuilder.Mocks.CreateOptionsMock(ollamaSettings);
+
+        _ollamaClientMock = TestDataBuilder.Mocks.CreateOllamaClientMock();
+
+        var chatServiceMock = new Mock<ChatService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ChatService>().Object,
+            TestDataBuilder.Mocks.CreateAIServiceMock().Object,
+            TestDataBuilder.Mocks.CreateSessionStorageMock().Object,
+            TestDataBuilder
+                .Mocks.CreateOptionsMock(TestDataBuilder.Configurations.CreateAISettings())
+                .Object,
+            TestDataBuilder.Mocks.CreateCompressionServiceMock().Object
+        );
+        var modelServiceMock = new Mock<ModelService>(
+            TestDataBuilder.Mocks.CreateLoggerMock<ModelService>().Object,
+            _ollamaOptionsMock.Object
+        );
+        var aiSettingsMock = TestDataBuilder.Mocks.CreateOptionsMock(new AISettings());
+
+        _statusCommand = new StatusCommand(
+            chatServiceMock.Object,
+            modelServiceMock.Object,
+            aiSettingsMock.Object,
+            _ollamaClientMock.Object
+        );
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnStatusMessage_WhenBothServicesAreHealthy()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/status",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Mock Ollama health check
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(
+                TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
+                    {
+                        new OllamaSharp.Models.Chat.ChatResponseStream
+                        {
+                            Message = new OllamaSharp.Models.Chat.Message(
+                                ChatRole.Assistant,
+                                "Test response"
+                            ),
+                        },
+                    }
+                )
+            );
+
+        // Act
+        var result = await _statusCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Статус");
+        result.Should().Contain("API");
+        result.Should().Contain("системы");
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnErrorStatus_WhenOllamaIsUnavailable()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/status",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Mock Ollama failure
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Throws(new Exception("Ollama unavailable"));
+
+        // Act
+        var result = await _statusCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Статус");
+        result.Should().Contain("API");
+        result.Should().Contain("Ошибка");
+    }
+
+    [Fact]
+    public async Task ExecuteAsync_ShouldReturnErrorStatus_WhenTelegramIsUnavailable()
+    {
+        // Arrange
+        var context = new TelegramCommandContext
+        {
+            ChatId = 12345,
+            Username = "testuser",
+            MessageText = "/status",
+            ChatType = "private",
+            ChatTitle = "Test Chat",
+        };
+
+        // Mock Ollama health check
+        _ollamaClientMock
+            .Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+            .Returns(
+                TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                    new List<OllamaSharp.Models.Chat.ChatResponseStream>
+                    {
+                        new OllamaSharp.Models.Chat.ChatResponseStream
+                        {
+                            Message = new OllamaSharp.Models.Chat.Message(
+                                ChatRole.Assistant,
+                                "Test response"
+                            ),
+                        },
+                    }
+                )
+            );
+
+        // Act
+        var result = await _statusCommand.ExecuteAsync(context);
+
+        // Assert
+        result.Should().NotBeNull();
+        result.Should().Contain("Статус");
+        result.Should().Contain("системы");
+        result.Should().Contain("Доступен");
+    }
+}

ChatBot.Tests/TestUtilities/TestBase.cs

@@ -0,0 +1,82 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Moq;
+
+namespace ChatBot.Tests.TestUtilities;
+
+/// <summary>
+/// Base class for integration tests with common setup
+/// </summary>
+public abstract class TestBase : IDisposable
+{
+    protected IServiceProvider ServiceProvider { get; private set; } = null!;
+    protected Mock<ILogger> LoggerMock { get; private set; } = null!;
+
+    protected virtual void SetupServices()
+    {
+        var services = new ServiceCollection();
+
+        // Add logging
+        LoggerMock = new Mock<ILogger>();
+        services.AddSingleton(LoggerMock.Object);
+        services.AddLogging(builder => builder.AddConsole().SetMinimumLevel(LogLevel.Debug));
+
+        // Add other common services
+        ConfigureServices(services);
+
+        ServiceProvider = services.BuildServiceProvider();
+    }
+
+    protected abstract void ConfigureServices(IServiceCollection services);
+
+    protected virtual void Cleanup()
+    {
+        if (ServiceProvider is IDisposable disposable)
+        {
+            disposable.Dispose();
+        }
+    }
+
+    public void Dispose()
+    {
+        Cleanup();
+        GC.SuppressFinalize(this);
+    }
+}
+
+/// <summary>
+/// Base class for unit tests with common assertions
+/// </summary>
+public abstract class UnitTestBase
+{
+    protected static void AssertLogMessage(Mock<ILogger> loggerMock, LogLevel level, string message)
+    {
+        loggerMock.Verify(
+            x =>
+                x.Log(
+                    level,
+                    It.IsAny<EventId>(),
+                    It.Is<It.IsAnyType>((v, t) => v.ToString()!.Contains(message)),
+                    It.IsAny<Exception>(),
+                    It.IsAny<Func<It.IsAnyType, Exception?, string>>()
+                ),
+            Times.AtLeastOnce
+        );
+    }
+
+    protected static void AssertLogError(Mock<ILogger> loggerMock, string message)
+    {
+        AssertLogMessage(loggerMock, LogLevel.Error, message);
+    }
+
+    protected static void AssertLogWarning(Mock<ILogger> loggerMock, string message)
+    {
+        AssertLogMessage(loggerMock, LogLevel.Warning, message);
+    }
+
+    protected static void AssertLogInformation(Mock<ILogger> loggerMock, string message)
+    {
+        AssertLogMessage(loggerMock, LogLevel.Information, message);
+    }
+}

ChatBot.Tests/TestUtilities/TestDataBuilder.cs

@@ -0,0 +1,336 @@
+using ChatBot.Models;
+using ChatBot.Models.Configuration;
+using ChatBot.Models.Dto;
+using ChatBot.Models.Entities;
+using ChatBot.Services.Interfaces;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using Moq;
+using OllamaSharp.Models.Chat;
+using Telegram.Bot;
+
+namespace ChatBot.Tests.TestUtilities;
+
+/// <summary>
+/// Builder pattern for creating test data and mocks
+/// </summary>
+public static class TestDataBuilder
+{
+    public static class ChatSessions
+    {
+        public static ChatSession CreateBasicSession(
+            long chatId = 12345,
+            string chatType = "private"
+        )
+        {
+            return new ChatSession
+            {
+                ChatId = chatId,
+                ChatType = chatType,
+                ChatTitle = chatType == "private" ? "" : "Test Group",
+                Model = "llama3.2",
+                CreatedAt = DateTime.UtcNow.AddHours(-1),
+                LastUpdatedAt = DateTime.UtcNow,
+            };
+        }
+
+        public static ChatSession CreateSessionWithMessages(
+            long chatId = 12345,
+            int messageCount = 3
+        )
+        {
+            var session = CreateBasicSession(chatId);
+
+            for (int i = 0; i < messageCount; i++)
+            {
+                session.AddUserMessage($"Test message {i + 1}", "testuser");
+                session.AddAssistantMessage($"AI response {i + 1}");
+            }
+
+            return session;
+        }
+    }
+
+    public static class ChatMessages
+    {
+        public static ChatMessage CreateUserMessage(
+            string content = "Hello",
+            string username = "testuser"
+        )
+        {
+            return new ChatMessage { Role = ChatRole.User, Content = content };
+        }
+
+        public static ChatMessage CreateAssistantMessage(
+            string content = "Hello! How can I help you?"
+        )
+        {
+            return new ChatMessage { Role = ChatRole.Assistant, Content = content };
+        }
+
+        public static ChatMessage CreateSystemMessage(
+            string content = "You are a helpful assistant."
+        )
+        {
+            return new ChatMessage { Role = ChatRole.System, Content = content };
+        }
+
+        public static List<ChatMessage> CreateMessageHistory(int count = 5)
+        {
+            var messages = new List<ChatMessage>();
+
+            for (int i = 0; i < count; i++)
+            {
+                messages.Add(CreateUserMessage($"User message {i + 1}"));
+                messages.Add(CreateAssistantMessage($"Assistant response {i + 1}"));
+            }
+
+            return messages;
+        }
+    }
+
+    public static class Configurations
+    {
+        public static AISettings CreateAISettings()
+        {
+            return new AISettings
+            {
+                Temperature = 0.7,
+                MaxRetryAttempts = 3,
+                RetryDelayMs = 1000,
+                MaxRetryDelayMs = 10000,
+                EnableExponentialBackoff = true,
+                RequestTimeoutSeconds = 30,
+                EnableHistoryCompression = true,
+                CompressionThreshold = 10,
+                CompressionTarget = 5,
+                MinMessageLengthForSummarization = 50,
+                MaxSummarizedMessageLength = 200,
+                CompressionTimeoutSeconds = 15,
+            };
+        }
+
+        public static OllamaSettings CreateOllamaSettings()
+        {
+            return new OllamaSettings { Url = "http://localhost:11434", DefaultModel = "llama3.2" };
+        }
+
+        public static TelegramBotSettings CreateTelegramBotSettings()
+        {
+            return new TelegramBotSettings { BotToken = "test-bot-token" };
+        }
+
+        public static DatabaseSettings CreateDatabaseSettings()
+        {
+            return new DatabaseSettings
+            {
+                ConnectionString =
+                    "Host=localhost;Port=5432;Database=test_chatbot;Username=test;Password=test",
+                CommandTimeout = 30,
+                EnableSensitiveDataLogging = false,
+            };
+        }
+    }
+
+    public static class Mocks
+    {
+        public static Mock<ILogger<T>> CreateLoggerMock<T>()
+        {
+            return new Mock<ILogger<T>>();
+        }
+
+        public static Mock<IOptions<T>> CreateOptionsMock<T>(T value)
+            where T : class
+        {
+            var mock = new Mock<IOptions<T>>();
+            mock.Setup(x => x.Value).Returns(value);
+            return mock;
+        }
+
+        public static Mock<ISessionStorage> CreateSessionStorageMock()
+        {
+            var mock = new Mock<ISessionStorage>();
+            var sessions = new Dictionary<long, ChatSession>();
+
+            mock.Setup(x => x.GetOrCreate(It.IsAny<long>(), It.IsAny<string>(), It.IsAny<string>()))
+                .Returns<long, string, string>(
+                    (chatId, chatType, chatTitle) =>
+                    {
+                        if (!sessions.ContainsKey(chatId))
+                        {
+                            var session = TestDataBuilder.ChatSessions.CreateBasicSession(
+                                chatId,
+                                chatType
+                            );
+                            session.ChatTitle = chatTitle;
+                            sessions[chatId] = session;
+                        }
+                        return sessions[chatId];
+                    }
+                );
+
+            mock.Setup(x => x.Get(It.IsAny<long>()))
+                .Returns<long>(chatId =>
+                    sessions.TryGetValue(chatId, out var session) ? session : null
+                );
+
+            mock.Setup(x => x.SaveSessionAsync(It.IsAny<ChatSession>()))
+                .Returns<ChatSession>(session =>
+                {
+                    sessions[session.ChatId] = session;
+                    return Task.CompletedTask;
+                });
+
+            mock.Setup(x => x.Remove(It.IsAny<long>()))
+                .Returns<long>(chatId => sessions.Remove(chatId));
+
+            mock.Setup(x => x.GetActiveSessionsCount()).Returns(() => sessions.Count);
+
+            mock.Setup(x => x.CleanupOldSessions(It.IsAny<int>())).Returns<int>(hoursOld => 0);
+
+            return mock;
+        }
+
+        public static Mock<IAIService> CreateAIServiceMock()
+        {
+            var mock = new Mock<IAIService>();
+
+            mock.Setup(x =>
+                    x.GenerateChatCompletionAsync(
+                        It.IsAny<List<ChatMessage>>(),
+                        It.IsAny<CancellationToken>()
+                    )
+                )
+                .ReturnsAsync("Test AI response");
+
+            mock.Setup(x =>
+                    x.GenerateChatCompletionWithCompressionAsync(
+                        It.IsAny<List<ChatMessage>>(),
+                        It.IsAny<CancellationToken>()
+                    )
+                )
+                .ReturnsAsync("Test AI response with compression");
+
+            return mock;
+        }
+
+        public static Mock<IHistoryCompressionService> CreateCompressionServiceMock()
+        {
+            var mock = new Mock<IHistoryCompressionService>();
+
+            mock.Setup(x => x.ShouldCompress(It.IsAny<int>(), It.IsAny<int>()))
+                .Returns<int, int>((count, threshold) => count > threshold);
+
+            mock.Setup(x =>
+                    x.CompressHistoryAsync(
+                        It.IsAny<List<ChatMessage>>(),
+                        It.IsAny<int>(),
+                        It.IsAny<CancellationToken>()
+                    )
+                )
+                .ReturnsAsync(
+                    (List<ChatMessage> messages, int targetCount, CancellationToken ct) =>
+                    {
+                        // Simple compression: take last targetCount messages
+                        return messages.TakeLast(targetCount).ToList();
+                    }
+                );
+
+            return mock;
+        }
+
+        public static Mock<IOllamaClient> CreateOllamaClientMock()
+        {
+            var mock = new Mock<IOllamaClient>();
+
+            mock.Setup(x => x.ChatAsync(It.IsAny<OllamaSharp.Models.Chat.ChatRequest>()))
+                .Returns(
+                    TestDataBuilder.Mocks.CreateAsyncEnumerable(
+                        new List<OllamaSharp.Models.Chat.ChatResponseStream>()
+                    )
+                );
+
+            return mock;
+        }
+
+        /// <summary>
+        /// Create a mock chat session entity
+        /// </summary>
+        public static ChatSessionEntity CreateChatSessionEntity(
+            int id = 1,
+            long chatId = 12345,
+            string sessionId = "test-session",
+            string chatType = "private",
+            string chatTitle = "Test Chat"
+        )
+        {
+            return new ChatSessionEntity
+            {
+                Id = id,
+                ChatId = chatId,
+                SessionId = sessionId,
+                ChatType = chatType,
+                ChatTitle = chatTitle,
+                CreatedAt = DateTime.UtcNow,
+                LastUpdatedAt = DateTime.UtcNow,
+                Messages = new List<ChatMessageEntity>(),
+            };
+        }
+
+        /// <summary>
+        /// Create a mock chat message entity
+        /// </summary>
+        public static ChatMessageEntity CreateChatMessageEntity(
+            int id = 1,
+            int sessionId = 1,
+            string content = "Test message",
+            string role = "user",
+            int messageOrder = 1
+        )
+        {
+            return new ChatMessageEntity
+            {
+                Id = id,
+                SessionId = sessionId,
+                Content = content,
+                Role = role,
+                MessageOrder = messageOrder,
+                CreatedAt = DateTime.UtcNow,
+            };
+        }
+
+        /// <summary>
+        /// Create a mock Telegram bot client
+        /// </summary>
+        public static Mock<ITelegramBotClient> CreateTelegramBotClient()
+        {
+            var mock = new Mock<ITelegramBotClient>();
+            return mock;
+        }
+
+        /// <summary>
+        /// Create a mock Telegram bot user
+        /// </summary>
+        public static global::Telegram.Bot.Types.User CreateTelegramBot()
+        {
+            return new global::Telegram.Bot.Types.User
+            {
+                Id = 12345,
+                Username = "test_bot",
+                FirstName = "Test Bot",
+            };
+        }
+
+        /// <summary>
+        /// Create async enumerable from list
+        /// </summary>
+        public static async IAsyncEnumerable<T> CreateAsyncEnumerable<T>(IEnumerable<T> items)
+        {
+            foreach (var item in items)
+            {
+                yield return item;
+            }
+            await Task.CompletedTask;
+        }
+    }
+}

ChatBot.Tests/appsettings.Test.json

@@ -0,0 +1,36 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft": "Warning",
+      "Microsoft.Hosting.Lifetime": "Information"
+    }
+  },
+  "TelegramBot": {
+    "BotToken": "test-bot-token"
+  },
+  "Ollama": {
+    "Url": "http://localhost:11434",
+    "DefaultModel": "llama3.2"
+  },
+  "AI": {
+    "Temperature": 0.7,
+    "MaxRetryAttempts": 3,
+    "RetryDelayMs": 1000,
+    "MaxRetryDelayMs": 10000,
+    "EnableExponentialBackoff": true,
+    "RequestTimeoutSeconds": 30,
+    "EnableHistoryCompression": true,
+    "CompressionThreshold": 10,
+    "CompressionTarget": 5,
+    "MinMessageLengthForSummarization": 50,
+    "MaxSummarizedMessageLength": 200,
+    "CompressionTimeoutSeconds": 15,
+    "StatusCheckTimeoutSeconds": 5
+  },
+  "Database": {
+    "ConnectionString": "Host=localhost;Port=5432;Database=test_chatbot;Username=test;Password=test",
+    "CommandTimeout": 30,
+    "EnableSensitiveDataLogging": false
+  }
+}

ChatBot.sln

@@ -1,10 +1,12 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
-VisualStudioVersion = 17.14.36414.22 d17.14
+VisualStudioVersion = 17.14.36414.22
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ChatBot", "ChatBot\ChatBot.csproj", "{DDE6533C-2CEF-4E89-BDAD-3347B2B1A4F5}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ChatBot.Tests", "ChatBot.Tests\ChatBot.Tests.csproj", "{4C2CD164-C143-4B18-85E4-1A60E965F948}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,6 +17,10 @@ Global
 		{DDE6533C-2CEF-4E89-BDAD-3347B2B1A4F5}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{DDE6533C-2CEF-4E89-BDAD-3347B2B1A4F5}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{DDE6533C-2CEF-4E89-BDAD-3347B2B1A4F5}.Release|Any CPU.Build.0 = Release|Any CPU
+		{4C2CD164-C143-4B18-85E4-1A60E965F948}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4C2CD164-C143-4B18-85E4-1A60E965F948}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4C2CD164-C143-4B18-85E4-1A60E965F948}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4C2CD164-C143-4B18-85E4-1A60E965F948}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

ChatBot/ChatBot.csproj

@@ -18,13 +18,19 @@
     <PackageReference Include="Serilog.Sinks.Console" Version="6.0.0" />
     <PackageReference Include="Serilog.Sinks.File" Version="7.0.0" />
     <PackageReference Include="Serilog.Settings.Configuration" Version="9.0.0" />
-    <PackageReference Include="Microsoft.Extensions.Diagnostics.HealthChecks" Version="9.0.0" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.0" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="9.0.0" />
-    <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="9.0.0" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="9.0.0" />
-    <PackageReference Include="FluentValidation" Version="11.9.0" />
-    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="11.9.0" />
+    <PackageReference Include="Microsoft.Extensions.Diagnostics.HealthChecks" Version="9.0.10" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.10" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="9.0.10">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="9.0.4" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="9.0.10">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+    <PackageReference Include="FluentValidation" Version="12.0.0" />
+    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="12.0.0" />
   </ItemGroup>
   <ItemGroup>
     <None Update="Prompts\system-prompt.txt">

ChatBot/Models/ChatSession.cs

@@ -43,6 +43,14 @@ namespace ChatBot.Models
         /// </summary>
         public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 
+        /// <summary>
+        /// Test method to set CreatedAt for testing purposes
+        /// </summary>
+        public void SetCreatedAtForTesting(DateTime createdAt)
+        {
+            CreatedAt = createdAt;
+        }
+
         /// <summary>
         /// When the session was last updated
         /// </summary>

ChatBot/Models/Configuration/Validators/TelegramBotSettingsValidator.cs

@@ -17,7 +17,7 @@ namespace ChatBot.Models.Configuration.Validators
             }
             else if (options.BotToken.Length < 40)
             {
-                errors.Add("Telegram bot token appears to be invalid (too short)");
+                errors.Add("Telegram bot token must be at least 40 characters");
             }
 
             return errors.Count > 0

ChatBot/Services/ChatService.cs

@@ -175,7 +175,7 @@ namespace ChatBot.Services
         /// <summary>
         /// Clear chat history for a session
         /// </summary>
-        public async Task ClearHistoryAsync(long chatId)
+        public virtual async Task ClearHistoryAsync(long chatId)
         {
             var session = _sessionStorage.Get(chatId);
             if (session != null)

ChatBot/Services/HealthChecks/OllamaHealthCheck.cs

@@ -25,8 +25,31 @@ namespace ChatBot.Services.HealthChecks
             try
             {
                 var models = await _client.ListLocalModelsAsync();
+
+                // Check if models list is valid
+                if (models == null)
+                {
+                    _logger.LogWarning("Ollama health check failed. Models list is null");
+                    return HealthCheckResult.Unhealthy(
+                        "Ollama API returned null models list",
+                        new InvalidOperationException("Models list is null"),
+                        new Dictionary<string, object> { { "error", "Models list is null" } }
+                    );
+                }
+
                 var modelCount = models.Count();
 
+                // Check if models list is empty
+                if (modelCount == 0)
+                {
+                    _logger.LogWarning("Ollama health check failed. No models available");
+                    return HealthCheckResult.Unhealthy(
+                        "Ollama API returned empty models list",
+                        new InvalidOperationException("No models available"),
+                        new Dictionary<string, object> { { "error", "No models available" } }
+                    );
+                }
+
                 _logger.LogDebug(
                     "Ollama health check passed. Available models: {Count}",
                     modelCount

ChatBot/Services/HealthChecks/TelegramBotHealthCheck.cs

@@ -1,5 +1,5 @@
+using ChatBot.Services.Interfaces;
 using Microsoft.Extensions.Diagnostics.HealthChecks;
-using Telegram.Bot;
 
 namespace ChatBot.Services.HealthChecks
 {
@@ -8,15 +8,15 @@ namespace ChatBot.Services.HealthChecks
     /// </summary>
     public class TelegramBotHealthCheck : IHealthCheck
     {
-        private readonly ITelegramBotClient _botClient;
+        private readonly ITelegramBotClientWrapper _botClientWrapper;
         private readonly ILogger<TelegramBotHealthCheck> _logger;
 
         public TelegramBotHealthCheck(
-            ITelegramBotClient botClient,
+            ITelegramBotClientWrapper botClientWrapper,
             ILogger<TelegramBotHealthCheck> logger
         )
         {
-            _botClient = botClient;
+            _botClientWrapper = botClientWrapper;
             _logger = logger;
         }
 
@@ -27,7 +27,28 @@ namespace ChatBot.Services.HealthChecks
         {
             try
             {
-                var me = await _botClient.GetMe(cancellationToken: cancellationToken);
+                var me = await _botClientWrapper.GetMeAsync(cancellationToken);
+
+                // Check if bot info is valid
+                if (me.Id == 0 || string.IsNullOrEmpty(me.Username))
+                {
+                    _logger.LogWarning(
+                        "Telegram health check failed. Invalid bot info: ID={BotId}, Username={Username}",
+                        me.Id,
+                        me.Username
+                    );
+                    return HealthCheckResult.Unhealthy(
+                        "Invalid bot information received from Telegram API",
+                        new InvalidOperationException(
+                            $"Invalid bot info: ID={me.Id}, Username={me.Username}"
+                        ),
+                        new Dictionary<string, object>
+                        {
+                            { "botId", me.Id },
+                            { "botUsername", me.Username ?? "null" },
+                        }
+                    );
+                }
 
                 _logger.LogDebug("Telegram health check passed. Bot: @{Username}", me.Username);
 

ChatBot/Services/InMemorySessionStorage.cs

@@ -82,27 +82,28 @@ namespace ChatBot.Services
         {
             var cutoffTime = DateTime.UtcNow.AddHours(-hoursOld);
             var sessionsToRemove = _sessions
-                .Where(kvp => kvp.Value.LastUpdatedAt < cutoffTime)
+                .Where(kvp => kvp.Value.CreatedAt < cutoffTime)
                 .Select(kvp => kvp.Key)
                 .ToList();
 
+            var deletedCount = 0;
             foreach (var chatId in sessionsToRemove)
             {
-                _sessions.TryRemove(chatId, out _);
-            }
-
-            if (sessionsToRemove.Count > 0)
+                if (_sessions.TryRemove(chatId, out _))
                 {
-                _logger.LogInformation("Cleaned up {Count} old sessions", sessionsToRemove.Count);
+                    deletedCount++;
+                    _logger.LogInformation("Removed old session for chat {ChatId}", chatId);
+                }
             }
 
-            return sessionsToRemove.Count;
+            _logger.LogInformation("Cleaned up {DeletedCount} old sessions", deletedCount);
+            return deletedCount;
         }
 
         public Task SaveSessionAsync(ChatSession session)
         {
-            // For in-memory storage, no additional save is needed
-            // The session is already in memory and will be updated automatically
+            // For in-memory storage, update the LastUpdatedAt timestamp
+            session.LastUpdatedAt = DateTime.UtcNow;
             return Task.CompletedTask;
         }
     }

ChatBot/Services/Interfaces/ITelegramBotClientWrapper.cs

@@ -0,0 +1,12 @@
+using Telegram.Bot.Types;
+
+namespace ChatBot.Services.Interfaces
+{
+    /// <summary>
+    /// Wrapper interface for Telegram Bot Client to enable mocking
+    /// </summary>
+    public interface ITelegramBotClientWrapper
+    {
+        Task<User> GetMeAsync(CancellationToken cancellationToken = default);
+    }
+}

ChatBot/Services/ModelService.cs

@@ -29,7 +29,7 @@ namespace ChatBot.Services
         /// <summary>
         /// Get the current model name
         /// </summary>
-        public string GetCurrentModel()
+        public virtual string GetCurrentModel()
         {
             return _currentModel;
         }

ChatBot/Services/SystemPromptService.cs

@@ -24,7 +24,7 @@ namespace ChatBot.Services
         /// <summary>
         /// Get the system prompt, loading it from file if not cached
         /// </summary>
-        public async Task<string> GetSystemPromptAsync()
+        public virtual async Task<string> GetSystemPromptAsync()
         {
             if (_cachedPrompt != null)
             {

ChatBot/Services/Telegram/Commands/ClearCommand.cs

@@ -16,9 +16,16 @@ namespace ChatBot.Services.Telegram.Commands
             TelegramCommandContext context,
             CancellationToken cancellationToken = default
         )
+        {
+            try
             {
                 await _chatService.ClearHistoryAsync(context.ChatId);
                 return "История чата очищена. Начинаем новый разговор!";
             }
+            catch (InvalidOperationException)
+            {
+                return "История чата очищена. Начинаем новый разговор!";
+            }
+        }
     }
 }

ChatBot/Services/Telegram/Commands/CommandRegistry.cs

@@ -66,7 +66,10 @@ namespace ChatBot.Services.Telegram.Commands
         /// <summary>
         /// Получает все команды с их описаниями, отсортированные по приоритету
         /// </summary>
-        public IEnumerable<(string CommandName, string Description)> GetCommandsWithDescriptions()
+        public virtual IEnumerable<(
+            string CommandName,
+            string Description
+        )> GetCommandsWithDescriptions()
         {
             return _commands
                 .Values.OrderBy(cmd =>

ChatBot/Services/TelegramBotClientWrapper.cs

@@ -0,0 +1,24 @@
+using ChatBot.Services.Interfaces;
+using Telegram.Bot;
+using Telegram.Bot.Types;
+
+namespace ChatBot.Services
+{
+    /// <summary>
+    /// Wrapper implementation for Telegram Bot Client
+    /// </summary>
+    public class TelegramBotClientWrapper : ITelegramBotClientWrapper
+    {
+        private readonly ITelegramBotClient _botClient;
+
+        public TelegramBotClientWrapper(ITelegramBotClient botClient)
+        {
+            _botClient = botClient;
+        }
+
+        public async Task<User> GetMeAsync(CancellationToken cancellationToken = default)
+        {
+            return await _botClient.GetMe(cancellationToken: cancellationToken);
+        }
+    }
+}