def test_containerWhereAllElementsAreKnown(self):
        """
        A L{crefutil._Container} where all of its elements are known at
        construction time is nonsensical and will result in errors in any call
        to addDependant.
        """
        container = crefutil._Container([1, 2, 3], list)
        self.assertRaises(AssertionError,
                          container.addDependant, {}, "ignore-me")

        A L{crefutil._Container} where all of its elements are known at
        construction time is nonsensical and will result in errors in any call
        to addDependant.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_persisted.py