def test_iterate(self):
        """
        A L{FlagConstant} instance which results from C{|} can be
        iterated upon to yield the original constants.
        """
        self.assertEqual(
            set(self.FXF.WRITE & self.FXF.READ),  # No flags
            set(()))
        self.assertEqual(
            set(self.FXF.WRITE),
            set((self.FXF.WRITE,)))
        self.assertEqual(
            set(self.FXF.WRITE | self.FXF.EXCLUSIVE),
            set((self.FXF.WRITE, self.FXF.EXCLUSIVE)))

        A L{FlagConstant} instance which results from C{|} can be
        iterated upon to yield the original constants.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_constants.py