def METHOD_NAME(arg, clean_astro_ui):
    """Ensure argument is a 2D array."""
    ui.load_arrays('bob', [1, 5], [1, 12], ui.Data1D)
    cmdl = ui.const1d.cmdl
    pmdl = ui.polynom1d.pmdl
    cmdl.c0 = 1.5
    pmdl.c0 = -5
    pmdl.c1 = 2
    ui.set_source('bob', cmdl + pmdl)
    ui.fit('bob')
    arglist = {'id': 'bob', 'error': True, 'niter': 100,
               arg: np.arange(3)}
    with pytest.raises(IOErr) as exc:
        ui.eqwidth(cmdl, cmdl + pmdl, **arglist)
    assert str(exc.value) == f'{arg} must be 2d numpy.ndarray'