def test_last():
colors = DoubleLinkedList()
colors.push("Cadmium Red Light")
assert colors.last() == "Cadmium Red Light"
colors.push("Hansa Yellow")
assert colors.last() == "Hansa Yellow"
colors.shift("Pthalo Green")
assert colors.last() == "Hansa Yellow"
def test_shift():
colors = DoubleLinkedList()
colors.shift("Cadmium Orange")
assert colors.count() == 1
colors.shift("Carbazole Violet")
assert colors.count() == 2
assert colors.pop() == "Cadmium Orange"
assert colors.count() == 1
assert colors.pop() == "Carbazole Violet"
assert colors.count() == 0
def test_unshift():
colors = DoubleLinkedList()
colors.shift("Viridian")
colors.shift("Sap Green")
colors.shift("Van Dyke")
assert colors.unshift() == "Van Dyke"
assert colors.unshift() == "Sap Green"
assert colors.unshift() == "Viridian"
assert colors.unshift() is None