@Override
  public synchronized List<UdfFactory> listFunctions() {
    return new ArrayList<>(udfs.values());
  }
@Test
  public void shouldHaveAllInitializedFunctionNamesInUppercase() {
    for (final UdfFactory udfFactory : functionRegistry.listFunctions()) {
      final String actual = udfFactory.getName();
      final String expected = actual.toUpperCase();

      assertThat("UDF name must be registered in uppercase", actual, equalTo(expected));
    }
  }