def METHOD_NAME(get_fn):
    with MDCRDTrajectoryFile(get_fn('frame0.mdcrd'), n_atoms=22) as f:
        xyz, box = f.read()
        assert box is None
    with MDCRDTrajectoryFile(get_fn('frame0.mdcrdbox'), n_atoms=22) as f:
        xyz2, box = f.read()
        eq(box.shape, (1002, 3))
        eq(xyz, xyz2)