from id import id

def test_id():
    x = []
    y = []
    i = id(x)
    assert i == i == id(x) == id(x)
    assert id(x) != id(y)
    del x
    assert i != id([])  # this systematically fails with CPython's built-in id()
    assert i != id([])

def test_obj():
    x = []
    assert id(x).obj is x