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test/Scry.Tests/ImagePreprocessorTests.cs

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+using Scry.Core.Imaging;
+using SkiaSharp;
+using Xunit;
+
+namespace Scry.Tests;
+
+public class ImagePreprocessorTests
+{
+    [Fact]
+    public void Resize_ProducesCorrectDimensions()
+    {
+        using var bitmap = CreateTestBitmap(100, 100);
+        
+        using var resized = ImagePreprocessor.Resize(bitmap, 32, 32);
+        
+        Assert.Equal(32, resized.Width);
+        Assert.Equal(32, resized.Height);
+    }
+    
+    [Fact]
+    public void ToGrayscale_ProducesGrayscaleImage()
+    {
+        using var bitmap = CreateColorBitmap(10, 10);
+        
+        using var grayscale = ImagePreprocessor.ToGrayscale(bitmap);
+        
+        Assert.Equal(10, grayscale.Width);
+        Assert.Equal(10, grayscale.Height);
+    }
+    
+    [Fact]
+    public void ApplyClahe_PreservesDimensions()
+    {
+        using var bitmap = CreateTestBitmap(64, 64);
+        
+        using var result = ImagePreprocessor.ApplyClahe(bitmap);
+        
+        Assert.Equal(64, result.Width);
+        Assert.Equal(64, result.Height);
+    }
+    
+    [Fact]
+    public void ApplyClahe_EnhancesContrast()
+    {
+        using var bitmap = CreateLowContrastBitmap(64, 64);
+        
+        using var result = ImagePreprocessor.ApplyClahe(bitmap);
+        
+        Assert.NotNull(result);
+        Assert.Equal(bitmap.Width, result.Width);
+        Assert.Equal(bitmap.Height, result.Height);
+    }
+    
+    [Theory]
+    [InlineData("varying_quality/test1.jpg")]
+    [InlineData("low_light/glare_toploader.png")]
+    [InlineData("foil/rainbow_foil_secret_lair.jpg")]
+    public void ApplyClahe_RealImages_DoesNotCrash(string imagePath)
+    {
+        var fullPath = Path.Combine("TestImages", imagePath);
+        if (!File.Exists(fullPath))
+        {
+            return;
+        }
+        
+        using var bitmap = SKBitmap.Decode(fullPath);
+        Assert.NotNull(bitmap);
+        
+        using var result = ImagePreprocessor.ApplyClahe(bitmap);
+        
+        Assert.Equal(bitmap.Width, result.Width);
+        Assert.Equal(bitmap.Height, result.Height);
+    }
+    
+    private static SKBitmap CreateTestBitmap(int width, int height)
+    {
+        var bitmap = new SKBitmap(width, height, SKColorType.Rgba8888, SKAlphaType.Premul);
+        using var canvas = new SKCanvas(bitmap);
+        canvas.Clear(SKColors.Gray);
+        return bitmap;
+    }
+    
+    private static SKBitmap CreateColorBitmap(int width, int height)
+    {
+        var bitmap = new SKBitmap(width, height, SKColorType.Rgba8888, SKAlphaType.Premul);
+        for (var y = 0; y < height; y++)
+        {
+            for (var x = 0; x < width; x++)
+            {
+                var r = (byte)(x * 255 / width);
+                var g = (byte)(y * 255 / height);
+                var b = (byte)((x + y) * 127 / (width + height));
+                bitmap.SetPixel(x, y, new SKColor(r, g, b));
+            }
+        }
+        return bitmap;
+    }
+    
+    private static SKBitmap CreateLowContrastBitmap(int width, int height)
+    {
+        var bitmap = new SKBitmap(width, height, SKColorType.Rgba8888, SKAlphaType.Premul);
+        for (var y = 0; y < height; y++)
+        {
+            for (var x = 0; x < width; x++)
+            {
+                var gray = (byte)(120 + (x + y) % 20);
+                bitmap.SetPixel(x, y, new SKColor(gray, gray, gray));
+            }
+        }
+        return bitmap;
+    }
+    
+    private static (byte Min, byte Max) GetLuminanceRange(SKBitmap bitmap)
+    {
+        byte min = 255;
+        byte max = 0;
+        
+        for (var y = 0; y < bitmap.Height; y++)
+        {
+            for (var x = 0; x < bitmap.Width; x++)
+            {
+                var pixel = bitmap.GetPixel(x, y);
+                var luminance = (byte)(0.299 * pixel.Red + 0.587 * pixel.Green + 0.114 * pixel.Blue);
+                min = Math.Min(min, luminance);
+                max = Math.Max(max, luminance);
+            }
+        }
+        
+        return (min, max);
+    }
+}