Update README.md to include project description, developer documentation links, and license information.

tests/MrGameEng.Graphics.Tests/SpriteBatcherTests.cs

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+using MrGameEng.Graphics;
+using Xunit;
+
+namespace MrGameEng.Graphics.Tests;
+
+public class SpriteBatcherTests
+{
+    private static SpriteInstance Instance(byte layer) => new() { Layer = layer };
+
+    [Fact]
+    public void Sort_OrdersByKey_ReturningOriginalIndices()
+    {
+        var batcher = new SpriteBatcher(initialCapacity: 2);
+
+        batcher.Submit(Instance(2), SpriteSortKey.Make(2, 0f, 0));
+        batcher.Submit(Instance(0), SpriteSortKey.Make(0, 0f, 0));
+        batcher.Submit(Instance(1), SpriteSortKey.Make(1, 0f, 0));
+
+        var order = batcher.Sort();
+
+        Assert.Equal(3, order.Length);
+        Assert.Equal(0, batcher[order[0]].Layer);
+        Assert.Equal(1, batcher[order[1]].Layer);
+        Assert.Equal(2, batcher[order[2]].Layer);
+    }
+
+    [Fact]
+    public void Submit_GrowsBeyondInitialCapacity()
+    {
+        var batcher = new SpriteBatcher(initialCapacity: 1);
+
+        for (var i = 0; i < 100; i++)
+        {
+            batcher.Submit(Instance(0), (ulong)(100 - i));
+        }
+
+        Assert.Equal(100, batcher.Count);
+        var order = batcher.Sort();
+        Assert.Equal(99, order[0]); // последний сабмит имеет наименьший ключ
+    }
+
+    [Fact]
+    public void Clear_ResetsCount_KeepsWorking()
+    {
+        var batcher = new SpriteBatcher();
+        batcher.Submit(Instance(0), 5);
+        batcher.Clear();
+
+        Assert.Equal(0, batcher.Count);
+        batcher.Submit(Instance(1), 1);
+        Assert.Equal(1, batcher.Count);
+        Assert.Equal(1, batcher[batcher.Sort()[0]].Layer);
+    }
+}