def METHOD_NAME(get_fn):
    traj = md.load(get_fn("tip3p_300K_1ATM.xtc"), top=get_fn("tip3p_300K_1ATM.pdb"))
    rho = md.geometry.density(traj).mean()
    reference = 973.651  # From gromacs, see above comment
    assert abs((rho - reference) / reference) < 1E-3, "Density tolerance not met!"