def test_popleft():
colors = SingleLinkedList()
colors.push('purple')
colors.push('green')
colors.push('yellow')
assert colors.popleft() == 'purple'
assert colors.popleft() == 'green'
assert colors.popleft() == 'yellow'
assert colors.popleft() == None
def test_dump():
colors = SingleLinkedList()
colors.push('red')
colors.push('white')
colors.push('blue')
colors.push('yellow')
assert colors.dump() == '[red, white, blue, yellow]'
colors.remove('white')
assert colors.dump() == '[red, blue, yellow]'
colors.pop()
assert colors.dump() == '[red, blue]'
colors.popleft()
assert colors.dump() == '[blue]'
