def METHOD_NAME(res):
    # Get material at first timestep
    step_result = res[0]
    mat1 = step_result.get_material("1")
    assert mat1.id == 1
    assert mat1.volume == step_result.volume["1"]
    # Spot check number densities
    densities = mat1.get_nuclide_atom_densities()
    assert densities['Xe135'] == pytest.approx(1e-14)
    assert densities['I135'] == pytest.approx(1e-21)
    assert densities['U234'] == pytest.approx(1.00506e-05)