def test_pop():
colors = DoubleLinkedList()
colors.push("Magenta")
colors._invariant()
colors.push("Alizarin")
colors.push("Van Dyke")
colors._invariant()
assert colors.pop() == "Van Dyke"
colors._invariant()
assert colors.get(1) == "Alizarin"
assert colors.pop() == "Alizarin"
assert colors.pop() == "Magenta"
colors._invariant()
assert colors.pop() is None
def test_get():
colors = DoubleLinkedList()
colors.push("Vermillion")
assert colors.get(0) == "Vermillion"
colors.push("Sap Green")
assert colors.get(0) == "Vermillion"
assert colors.get(1) == "Sap Green"
colors.push("Cadmium Yellow Light")
assert colors.get(0) == "Vermillion"
assert colors.get(1) == "Sap Green"
assert colors.get(2) == "Cadmium Yellow Light"
assert colors.pop() == "Cadmium Yellow Light"
assert colors.get(0) == "Vermillion"
assert colors.get(1) == "Sap Green"
assert colors.get(2) is None
colors.pop()
assert colors.get(0) == "Vermillion"
colors.pop()
assert colors.get(0) is None