Add missing unit tests

tests/ImageSharp.Tests/Drawing/DrawImageTest.cs

@@ -9,6 +9,8 @@ using Xunit;
 
 namespace SixLabors.ImageSharp.Tests
 {
+    using System;
+
     public class DrawImageTest : FileTestBase
     {
         private const PixelTypes PixelTypes = Tests.PixelTypes.Rgba32;
@@ -42,5 +44,45 @@ namespace SixLabors.ImageSharp.Tests
                 image.DebugSave(provider, new { mode });
             }
         }
+
+        [Theory]
+        [WithFile(TestImages.Bmp.Car, PixelTypes.Rgba32, TestImages.Png.Splash)]
+        public void ImageShouldHandleNegativeLocation(TestImageProvider<Rgba32> provider, string backgroundPath)
+        {
+            using (Image<Rgba32> background = TestFile.Create(backgroundPath).CreateImage())
+            using (Image<Rgba32> overlay = provider.GetImage())
+            {
+                int xy = -25;
+                Rgba32 backgroundPixel = background[0, 0];
+                Rgba32 overlayPixel = overlay[Math.Abs(xy) + 1, Math.Abs(xy) + 1];
+
+                background.Mutate(x => x.DrawImage(overlay, PixelBlenderMode.Normal, 1F, new Size(overlay.Width, overlay.Height), new Point(xy, xy)));
+
+                Assert.Equal(default(Rgba32), backgroundPixel);
+                Assert.Equal(overlayPixel, background[0, 0]);
+
+                background.DebugSave(provider, new[] { "Negative" });
+            }
+        }
+
+        [Theory]
+        [WithFile(TestImages.Bmp.Car, PixelTypes.Rgba32, TestImages.Png.Splash)]
+        public void ImageShouldHandlePositiveLocation(TestImageProvider<Rgba32> provider, string backgroundPath)
+        {
+            using (Image<Rgba32> background = TestFile.Create(backgroundPath).CreateImage())
+            using (Image<Rgba32> overlay = provider.GetImage())
+            {
+                int xy = 25;
+                Rgba32 backgroundPixel = background[xy - 1, xy - 1];
+                Rgba32 overlayPixel = overlay[0, 0];
+
+                background.Mutate(x => x.DrawImage(overlay, PixelBlenderMode.Normal, 1F, new Size(overlay.Width, overlay.Height), new Point(xy, xy)));
+
+                Assert.Equal(default(Rgba32), backgroundPixel);
+                Assert.Equal(overlayPixel, background[xy, xy]);
+
+                background.DebugSave(provider, new[] { "Positive" });
+            }
+        }
     }
 }