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
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
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_remove():
colors = DoubleLinkedList()
colors.push("Cobalt")
colors.push("Zinc White")
colors.push("Nickle Yellow")
colors.push("Perinone")
assert colors.remove("Cobalt") == 0
colors._invariant()
colors.dump("before perinone")
assert colors.remove("Perinone") == 2
colors._invariant()
colors.dump("after perinone")
assert colors.remove("Nickle Yellow") == 1
colors._invariant()
assert colors.remove("Zinc White") == 0
colors._invariant()
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_push():
colors = DoubleLinkedList()
colors.push("Pthalo Blue")
colors._invariant()
assert colors.count() == 1
colors.push("Ultramarine Blue")
assert colors.count() == 2
colors._invariant()
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