@property
    def dummy_client(self):
        raise NotImplementedError("Subclasses must implement this function.")
Test that _Diff includes the delta in the error msg.
dataset/ETHPy150Open idan/oauthlib/oauthlib/oauth1/rfc5849/request_validator.py/RequestValidator.dummy_client--crossover with--dataset/ETHPy150Open google/google-apputils/tests/basetest_test.py/GoogleTestBaseUnitTest.test_Diff_Exception