def test_membership(self):
        """
        A L{FlagConstant} instance which results from C{|} can be
        tested for membership.
        """
        flags = self.FXF.WRITE | self.FXF.EXCLUSIVE
        self.assertIn(self.FXF.WRITE, flags)
        self.assertNotIn(self.FXF.READ, flags)

        A L{FlagConstant} instance which results from C{|} can be
        tested for membership.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_constants.py