def METHOD_NAME():
    """
    checks that there is no vertical movement
    """
    mv = RandomMover3D(mixed_layer_depth=10.0) # mostly defaults
    num_elements = 100
    sc = sample_sc_release(num_elements=num_elements,
                           start_pos=(0.0, 0.0, 0.0),
                           release_time=model_time,
                           )
    # set z positions:
    sc['positions'][:, 2] = np.linspace(0, 50, num_elements)
    print(sc['positions'])
    mv.vertical_diffusion_coef_above_ml = 0.0
    mv.vertical_diffusion_coef_below_ml = 0.0
    delta = mv.get_move(sc,
                        time_step,
                        model_time,
                        )
    print(delta)
    assert not np.alltrue(delta[:, 2] == 0.0)