Answer getRegisterMessageStreamAnswer() {
    return (InvocationOnMock x) -> {
      Integer id = x.getArgumentAt(0, Integer.class);
      MessageStream stream = x.getArgumentAt(1, MessageStream.class);
      registeredStreams.put(id, stream);
      return null;
    };
  }
Base class for all unit tests for translators
samza-sql/src/test/java/org/apache/samza/sql/translator/TranslatorTestBase.java