This work around no longer necessary,

... as the newer Groovy compiler produces the proper enclosing class
infromation.

test/src/main/java/org/jvnet/hudson/test/TestExtensionLoader.java

@@ -72,11 +72,6 @@ public class TestExtensionLoader extends GuiceExtensionAnnotation<TestExtension>
                     return true;      // enclosed
                 }
             }
-
-            // Groovy compiler doesn't seem to put the enclosing class information in the class file,
-            // so this fallback rule would catch those cases.
-            if (((Class)e).getName().startsWith(className+"$"))
-                return true;
             return false;
         }
         if (e instanceof Field) {