def METHOD_NAME(get_fn, time_diff):
    # Check if the tail of g(r,t) at t=0 and t=time_diff is normalized to ~1.0
    traj = md.load(get_fn('tip3p_300K_1ATM.xtc'), top=get_fn('tip3p_300K_1ATM.pdb'))
    times = list()
    for j in range(100):
        if (j + time_diff) > traj.n_frames:
            continue
        times.append([j, j+time_diff])
    pairs = traj.top.select_pairs('name O', 'name O')
    r_t, rdf_O_O = mdtraj.geometry.rdf.compute_rdf_t(traj, pairs, times)
    assert eq(np.ones(20), np.mean(rdf_O_O, axis=0)[-20:], decimal=1)
    pairs = traj.top.select_pairs('name O', "name =~ 'H.*'")
    r_t, rdf_O_H = mdtraj.geometry.rdf.compute_rdf_t(traj, pairs, times)
    assert eq(np.ones(20), np.mean(rdf_O_H, axis=0)[-20:], decimal=1)