def METHOD_NAME(ph_nacl: Phonopy):
    """Test displacements of NaCl 2x2x2."""
    dataset = deepcopy(ph_nacl.dataset)
    disp_ref = [[0, 0.01, 0.0, 0.0], [32, 0.01, 0.0, 0.0]]
    np.testing.assert_allclose(ph_nacl.displacements, disp_ref, atol=1e-8)
    ph_nacl.generate_displacements()
    np.testing.assert_allclose(ph_nacl.displacements, disp_ref, atol=1e-8)
    ph_nacl.dataset = dataset