def test_hashability(self):
        """
        In order for one test method to be runnable twice, two TestCase
        instances with the same test method name should not have the same
        hash value.
        """
        container = {}
        container[self.first] = None
        container[self.second] = None
        self.assertEqual(len(container), 2)

        In order for one test method to be runnable twice, two TestCase
        instances with the same test method name should not have the same
        hash value.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_testcase.py