def METHOD_NAME(self, ethane, hexane):
    port = mb.Port(anchor=ethane, separation=0.7)
    port.update_separation(separation=0.9)
    assert np.allclose(0.9, port.separation, atol=1e-15)
    port_used = hexane.labels["propyl2"].labels["down"]
    with pytest.warns(UserWarning):
        port_used.update_separation(0.10)