def test_diff_interface_stability(self):
        """Test that the Diffable.Index redefinition should not break compatibility."""
        self.assertIs(
            Diffable.Index,
            Diffable.INDEX,
            "The old and new class attribute names must be aliases.",
        )
        self.assertIs(
            type(Diffable.INDEX).__eq__,
            object.__eq__,
            "Equality comparison must be reference-based.",
        )
Test that the Diffable.Index redefinition should not break compatibility.
test/test_diff.py