def METHOD_NAME(traj):
    # Check that extracting a specific index works
    traj, in_fn, tmpdir = traj
    out_fn = '{}/frame4.pdb'.format(tmpdir)
    subprocess.check_call(['mdconvert', in_fn, '-i', '4', '-o', out_fn])
    frame4 = md.load(out_fn)
    eq(frame4.xyz, traj[4].xyz)