def METHOD_NAME(self):
    """
    checks that there is no movement if z below surface
    """
    num_elements = 10
    sc = sample_sc_release(num_elements=num_elements,
                           start_pos=(0.0, 0.0, 0.0),
                           release_time=self.model_time,
                           )
    # set z positions:
    sc['positions'][:, 2] = 100
    delta = self.mover.get_move(sc,
                                self.time_step,
                                self.model_time,
                                )
    print(delta)
    assert np.alltrue(delta[:, :] == 0.0)