from stack import Stack


def test_push():
    colors = Stack()
    colors.push("Pthalo Blue")
    assert colors.count() == 1
    colors.push("Ultramarine Blue")
    assert colors.count() == 2


def test_pop():
    colors = Stack()
    colors.push("Magenta")
    colors.push("Alizarin")
    assert colors.pop() == "Alizarin"
    assert colors.count() == 1
    assert colors.pop() == "Magenta"
    assert colors.count() == 0
    assert colors.pop() is None


def test_top():
    colors = Stack()
    colors.push("Cadmium Red Light")
    assert colors.top() == "Cadmium Red Light"
    colors.push("Hansa Yellow")
    assert colors.top() == "Hansa Yellow"
    colors.pop()
    assert colors.top() == "Cadmium Red Light"
    colors.pop()
    assert colors.top() is None