Add unit tests

tests/ImageSharp.Tests/Image/ImageTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.PixelFormats;
@@ -109,5 +110,64 @@ namespace SixLabors.ImageSharp.Tests
                 Assert.Equal("image/png", mime.DefaultMimeType);
             }
         }
+
+        [Theory]
+        [WithTestPatternImages(10, 10, PixelTypes.Rgba32)]
+        public void CloneFrame<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> img = provider.GetImage())
+            {
+                img.Frames.Add(new ImageFrame<TPixel>(10, 10));// add a frame anyway
+                using (Image<TPixel> cloned = img.Clone(0))
+                {
+                    Assert.Equal(2, img.Frames.Count);
+                    cloned.ComparePixelBufferTo(img.GetPixelSpan());
+                }
+            }
+        }
+
+        [Theory]
+        [WithTestPatternImages(10, 10, PixelTypes.Rgba32)]
+        public void CloneFrameAs<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> img = provider.GetImage())
+            {
+                img.Frames.Add(new ImageFrame<TPixel>(10, 10));// add a frame anyway
+                using (Image<Bgra32> cloned = img.CloneAs<Bgra32>(0))
+                {
+                    for (var x = 0; x < img.Width; x++)
+                    {
+                        for (var y = 0; y < img.Height; y++)
+                        {
+                            Bgra32 pixelClone = cloned[x, y];
+                            Bgra32 pixelSource = default(Bgra32);
+                            img[x, y].ToBgra32(ref pixelSource);
+                            Assert.Equal(pixelSource, pixelClone);
+                        }
+                    }
+                    Assert.Equal(2, img.Frames.Count);
+                }
+            }
+        }
+
+        [Theory]
+        [WithTestPatternImages(10, 10, PixelTypes.Rgba32)]
+        public void ExtractFrame<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : struct, IPixel<TPixel>
+        {
+            using (Image<TPixel> img = provider.GetImage())
+            {
+                var sourcePixelData = img.GetPixelSpan().ToArray();
+
+                img.Frames.Add(new ImageFrame<TPixel>(10, 10));
+                using (Image<TPixel> cloned = img.Extract(0))
+                {
+                    Assert.Equal(1, img.Frames.Count);
+                    cloned.ComparePixelBufferTo(sourcePixelData);
+                }
+            }
+        }
     }
 }

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

@@ -77,6 +77,11 @@ namespace SixLabors.ImageSharp.Tests
                 int top = 0;
                 int bottom = pixels.Height / 2;
                 int stride = pixels.Width / 12;
+                if (stride < 1)
+                {
+                    stride = 1;
+                }
+
                 TPixel[] c = {
                                      NamedColors<TPixel>.HotPink,
                                      NamedColors<TPixel>.Blue
@@ -197,14 +202,14 @@ namespace SixLabors.ImageSharp.Tests
                 Rgba32 t = new Rgba32(0);
 
                 for (int x = left; x < right; x++)
-                for (int y = top; y < bottom; y++)
-                {
-                    t.PackedValue += stepsPerPixel;
-                    Vector4 v = t.ToVector4();
-                    //v.W = (x - left) / (float)left;
-                    c.PackFromVector4(v);
-                    pixels[x, y] = c;
-                }
+                    for (int y = top; y < bottom; y++)
+                    {
+                        t.PackedValue += stepsPerPixel;
+                        Vector4 v = t.ToVector4();
+                        //v.W = (x - left) / (float)left;
+                        c.PackFromVector4(v);
+                        pixels[x, y] = c;
+                    }
             }
         }
     }