def test_molar_mass_amu(): x = 1 * (u.g/u.mol) y = 1 * u.u assert_allclose(x.to_value(u.u, u.molar_mass_amu()), y.value) assert_allclose(y.to_value(u.g/u.mol, u.molar_mass_amu()), x.value) with pytest.raises(u.UnitsError): x.to(u.u)