Add user creation functionality: implement API endpoint for creating new users, including request handling and response management. Update frontend to support user creation with a new form in the UsersPanel, integrating role selection and input validation. Enhance i18n for new user-related strings.

backend/tests/TeleWave.Application.Tests/Admin/Users/CreateUserCommandHandlerTests.cs

@@ -0,0 +1,54 @@
+using NSubstitute;
+using TeleWave.Application.Admin.Roles;
+using TeleWave.Application.Admin.Users.CreateUser;
+using TeleWave.Application.Common.Interfaces;
+using TeleWave.Application.Common.Models;
+using Xunit;
+
+namespace TeleWave.Application.Tests.Admin.Users;
+
+public class CreateUserCommandHandlerTests
+{
+    private readonly IIdentityService _identityService = Substitute.For<IIdentityService>();
+    private readonly IRoleService _roleService = Substitute.For<IRoleService>();
+
+    private CreateUserCommandHandler CreateHandler() => new(_identityService, _roleService);
+
+    [Fact]
+    public async Task Handle_WithValidRole_CreatesUserAndAssignsRole()
+    {
+        var roleId = Guid.NewGuid();
+        var userId = Guid.NewGuid();
+        _roleService
+            .ListRolesAsync(Arg.Any<CancellationToken>())
+            .Returns(new List<RoleDto> { new(roleId, "user", true) });
+        _identityService
+            .CreateUserAsync("bob", "Password1", Arg.Any<CancellationToken>())
+            .Returns(Result.Success(userId));
+        _roleService
+            .ChangeUserRoleAsync(userId, roleId, Arg.Any<CancellationToken>())
+            .Returns(Result.Success());
+
+        var result = await CreateHandler()
+            .Handle(new CreateUserCommand("bob", "Password1", roleId), CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal(userId, result.Value);
+        await _roleService.Received(1).ChangeUserRoleAsync(userId, roleId, Arg.Any<CancellationToken>());
+    }
+
+    [Fact]
+    public async Task Handle_WithUnknownRole_ReturnsNotFoundAndDoesNotCreate()
+    {
+        _roleService.ListRolesAsync(Arg.Any<CancellationToken>()).Returns(new List<RoleDto>());
+
+        var result = await CreateHandler()
+            .Handle(new CreateUserCommand("bob", "Password1", Guid.NewGuid()), CancellationToken.None);
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(RoleErrors.NotFound, result.Error);
+        await _identityService
+            .DidNotReceive()
+            .CreateUserAsync(Arg.Any<string>(), Arg.Any<string>(), Arg.Any<CancellationToken>());
+    }
+}