def METHOD_NAME(get_fn):
    # Read a binpos with stride=3 when n_frames is supplied (different code path)
    fn_binpos = get_fn('frame0.binpos')
    with BINPOSTrajectoryFile(fn_binpos) as f:
        xyz = f.read(n_frames=1000, stride=3)
    xyz2 = io.loadh(get_fn('frame0.binpos.h5'), 'xyz')
    assert eq(xyz, xyz2[::3])