code: public static <T> OngoingStubbing<T> when(Class<?> klass, Object... arguments) throws Exception {
          return Mockito.when(Whitebox.<T>invokeMethod(klass, arguments));
      }
docs: Expect calls to private static methods without having to specify the
  method name. The method will be looked up using the parameter types if
  possible
  
  @throws Exception If something unexpected goes wrong.
  @see PowerMockito#when(Object)