def assertSuitesEqual(self, observed, expected):
        """
        Assert that the given test suites with decorated tests are equal.
        """
        self.assertEqual(observed.__class__, expected.__class__,
                         "Different class")
        self.assertEqual(len(observed._tests), len(expected._tests),
                         "Different number of tests.")
        for observedTest, expectedTest in zip(observed._tests,
                                              expected._tests):
            if getattr(observedTest, '_tests', None) is not None:
                self.assertSuitesEqual(observedTest, expectedTest)
            else:
                self.assertTestsEqual(observedTest, expectedTest)

        Assert that the given test suites with decorated tests are equal.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_tests.py