add more test cases

src/libraries/System.Runtime.InteropServices.RuntimeInformation/tests/CheckPlatformTests.cs

@@ -263,6 +263,9 @@ public void PlatformNamesAreComparedUsingOrdinalIgnoreCase()
         public void OSX_equals_macOS()
         {
             Assert.Equal(OSPlatform.OSX, OSPlatform.macOS);
+            Assert.Equal(OSPlatform.OSX, OSPlatform.Create("macOS"));
+            Assert.Equal(OSPlatform.Create("OSX"), OSPlatform.macOS);
+            Assert.Equal(OSPlatform.Create("OSX"), OSPlatform.Create("macOS"));
         }
     }
 }