Use Path.DirectorySeparatorChar

tests/ImageSharp.Tests/Formats/GeneralFormatTests.cs

@@ -171,7 +171,7 @@ namespace SixLabors.ImageSharp.Tests.Formats
 
                 using (var image2 = Image.Load<Rgba32>(serialized))
                 {
-                    image2.Save($"{path}/{file.FileName}");
+                    image2.Save($"{path}{Path.DirectorySeparatorChar}{file.FileName}");
                 }
             }
         }

tests/ImageSharp.Tests/TestUtilities/ImagingTestCaseUtility.cs

@@ -97,7 +97,7 @@ namespace SixLabors.ImageSharp.Tests
                 details = '_' + details;
             }
 
-            return TestUtils.AsInvariantString($"{this.GetTestOutputDir()}/{this.TestName}{pixName}{fn}{details}{extension}");
+            return TestUtils.AsInvariantString($"{this.GetTestOutputDir()}{Path.DirectorySeparatorChar}{this.TestName}{pixName}{fn}{details}{extension}");
         }
 
         /// <summary>