introduce [WithBasicTestPatternImages]

tests/ImageSharp.Tests/Processing/Processors/Transforms/ResizeTests.cs

@@ -35,6 +35,23 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
 
         private const PixelTypes CommonNonDefaultPixelTypes =
             PixelTypes.Rgba32 | PixelTypes.Bgra32 | PixelTypes.RgbaVector;
+        
+        [Theory]
+        [WithBasicTestPatternImages(15, 12, PixelTypes.Rgba32)]
+        public void Resize_BasicSmall<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            // Basic test case, very helpful for debugging
+            // resizing: (15, 12) -> (10, 6)
+            // kernel dimensions: (3, 4)
+
+            using (Image<TPixel> image = provider.GetImage())
+            {
+                var destSize = new Size(image.Width * 2 / 3, image.Height / 2);
+                image.Mutate(x => x.Resize(destSize, KnownResamplers.Bicubic, false));
+                image.DebugSave(provider);
+            }
+        }
 
         [Theory]
         [WithFileCollection(nameof(CommonTestImages), nameof(AllResamplerNames), DefaultPixelType, 0.5f, null, null)]

tests/ImageSharp.Tests/TestUtilities/Attributes/WithBasicTestPatternImagesAttribute.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Reflection;
+
+namespace SixLabors.ImageSharp.Tests
+{
+    public class WithBasicTestPatternImagesAttribute : ImageDataAttributeBase
+    {
+        public WithBasicTestPatternImagesAttribute(int width, int height, PixelTypes pixelTypes, params object[] additionalParameters)
+            : this(null, width, height, pixelTypes, additionalParameters)
+        {
+        }
+
+        public WithBasicTestPatternImagesAttribute(string memberData, int width, int height, PixelTypes pixelTypes, params object[] additionalParameters)
+            : base(memberData, pixelTypes, additionalParameters)
+        {
+            this.Width = width;
+            this.Height = height;
+        }
+
+        /// <summary>
+        /// Gets the width
+        /// </summary>
+        public int Width { get; }
+
+        /// <summary>
+        /// Gets the height
+        /// </summary>
+        public int Height { get; }
+
+        protected override string GetFactoryMethodName(MethodInfo testMethod) => "BasicTestPattern";
+
+        protected override object[] GetFactoryMethodArgs(MethodInfo testMethod, Type factoryType) => new object[] { this.Width, this.Height };
+    }
+}

tests/ImageSharp.Tests/TestUtilities/ImageProviders/BasicTestPatternProvider.cs

@@ -0,0 +1,65 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Numerics;
+
+using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Tests
+{
+    public abstract partial class TestImageProvider<TPixel>
+    {
+        private class BasicTestPatternProvider : BlankProvider
+        {
+            public BasicTestPatternProvider(int width, int height)
+                : base(width, height)
+            {
+            }
+
+            /// <summary>
+            /// This parameterless constructor is needed for xUnit deserialization
+            /// </summary>
+            public BasicTestPatternProvider()
+            {
+            }
+
+            public override string SourceFileOrDescription => TestUtils.AsInvariantString($"BasicTestPattern{this.Width}x{this.Height}");
+
+            public override Image<TPixel> GetImage()
+            {
+                var result = new Image<TPixel>(this.Width, this.Height);
+
+                TPixel topLeftColor = NamedColors<TPixel>.Red;
+                TPixel topRightColor = NamedColors<TPixel>.Green;
+                TPixel bottomLeftColor = NamedColors<TPixel>.Blue;
+
+                // Transparent purple:
+                TPixel bottomRightColor = default;
+                bottomRightColor.FromVector4(new Vector4(1f, 0f, 1f, 0.5f));
+
+                int midY = this.Height / 2;
+                int midX = this.Width / 2;
+
+                for (int y = 0; y < midY; y++)
+                {
+                    Span<TPixel> row = result.GetPixelRowSpan(y);
+
+                    row.Slice(0, midX).Fill(topLeftColor);
+                    row.Slice(midX, this.Width-midX).Fill(topRightColor);
+                }
+
+                for (int y = midY; y < this.Height; y++)
+                {
+                    Span<TPixel> row = result.GetPixelRowSpan(y);
+
+                    row.Slice(0, midX).Fill(bottomLeftColor);
+                    row.Slice(midX, this.Width-midX).Fill(bottomRightColor);
+                }
+
+                return result;
+            }
+        }
+    }
+}

tests/ImageSharp.Tests/TestUtilities/ImageProviders/BlankProvider.cs

@@ -20,6 +20,9 @@ namespace SixLabors.ImageSharp.Tests
                 this.Height = height;
             }
 
+            /// <summary>
+            /// This parameterless constructor is needed for xUnit deserialization
+            /// </summary>
             public BlankProvider()
             {
                 this.Width = 100;

tests/ImageSharp.Tests/TestUtilities/ImageProviders/SolidProvider.cs

@@ -35,6 +35,9 @@ namespace SixLabors.ImageSharp.Tests
                 this.a = a;
             }
 
+            /// <summary>
+            /// This parameterless constructor is needed for xUnit deserialization
+            /// </summary>
             public SolidProvider()
                 : base()
             {

tests/ImageSharp.Tests/TestUtilities/ImageProviders/TestImageProvider.cs

@@ -44,6 +44,12 @@ namespace SixLabors.ImageSharp.Tests
         public string MethodName { get; private set; }
         public string OutputSubfolderName { get; private set; }
 
+        public static TestImageProvider<TPixel> BasicTestPattern(int width,
+                                                                 int height,
+                                                                 MethodInfo testMethod = null,
+                                                                 PixelTypes pixelTypeOverride = PixelTypes.Undefined)
+            => new BasicTestPatternProvider(width, height).Init(testMethod, pixelTypeOverride);
+
         public static TestImageProvider<TPixel> TestPattern(
                 int width,
                 int height,

tests/ImageSharp.Tests/TestUtilities/ImageProviders/TestPatternProvider.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Net.Mime;
 using System.Numerics;
 
 using SixLabors.ImageSharp.Memory;
@@ -25,8 +26,10 @@ namespace SixLabors.ImageSharp.Tests
             {
             }
 
+            /// <summary>
+            /// This parameterless constructor is needed for xUnit deserialization
+            /// </summary>
             public TestPatternProvider()
-                : base()
             {
             }
 

tests/ImageSharp.Tests/TestUtilities/Tests/TestImageProviderTests.cs

@@ -325,6 +325,20 @@ namespace SixLabors.ImageSharp.Tests
             }
         }
 
+        [Theory]
+        [WithBasicTestPatternImages(50, 100, PixelTypes.Rgba32)]
+        [WithBasicTestPatternImages(49,17, PixelTypes.Rgba32)]
+        [WithBasicTestPatternImages(20, 10, PixelTypes.Rgba32)]
+        public void Use_WithBasicTestPatternImages<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> img = provider.GetImage())
+            {
+                img.DebugSave(provider);
+            }
+        }
+
+
         public static readonly TheoryData<object> BasicData = new TheoryData<object>()
         {
             TestImageProvider<Rgba32>.Blank(10, 20),