@classmethod
def assert_equal(cls, old, new):
    """
        This method is used by asdf to test that to_tree > from_tree gives an
        equivalent object.
        """
    assert old.meta == new.meta
    cls._assert_wcs_equal(old.wcs, new.wcs)
    cls._assert_table_equal(old.headers, new.headers)
    ac_new = new._array_container.external_array_references
    ac_old = old._array_container.external_array_references
    assert ac_new == ac_old
    assert old.unit == new.unit
    assert old.mask == new.mask
