def test_composite_create(self):
        potential = self.Cls()

        # Add a point mass with same unit system
        potential["one"] = KeplerPotential(units=self.units, m=1.)

        with pytest.raises(TypeError):
            potential["two"] = "derp"

        assert "one" in potential.parameters
        assert "m" in potential.parameters["one"]
        with pytest.raises(TypeError):
            potential.parameters["m"] = "derp"