@Override
  public synchronized List<UdfFactory> listFunctions() {
    return new ArrayList<>(udfs.values());
  }
@Test
  public void shouldHaveNoBuiltInUDFsRegistered() {
    final Collection<String> names = Collections2.transform(functionRegistry.listFunctions(),
        UdfFactory::getName);

    assertThat("One or more built-in Kudfs are registered in the InternalFunctionRegistry",
        names, hasSize(0));
  }