Update DiffRunnerTests.cs

Author: SimonCropp

src/DiffEngine.Tests/DiffRunnerTests.cs

@@ -1,5 +1,7 @@
-using System.IO;
+using System;
+using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Threading;
 using DiffEngine;
 using Xunit;
@@ -35,6 +37,10 @@ public void Kill()
     [Fact]
     public void LaunchAndKill()
     {
+        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            return;
+        }
         DiffTools.AddCustomTool(
             supportsAutoRefresh: true,
             isMdi: false,