def METHOD_NAME():
    cells = [openmc.Cell() for i in range(5)]
    cells2 = [openmc.Cell() for i in range(3)]
    cells[0].fill = openmc.Universe(cells=cells2)
    u = openmc.Universe(cells=cells)
    assert not (set(u.cells.values()) ^ set(cells))
    all_cells = set(u.get_all_cells().values())
    assert not (all_cells ^ set(cells + cells2))