def test_one_push_two_node():
stack = Stack()
stack.push('a')
stack.push('b')
expected = 'b'
actual = stack.top.value
assert actual == expected
def test_stack_pop_multiple():
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
assert stack.pop() == 3
assert stack.pop() == 2
assert stack.pop() == 1
def test_stack_push():
stack = Stack()
stack.push(1)
assert stack.top.data== 1
def test_stack_peek():
stack = Stack()
stack.push(1)
stack.push(2)
assert stack.peek() == 2
def test_stack_push_multiple():
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)
assert stack.top.data == 3
def test_one_push_one_node():
stack = Stack()
expected = 'a'
stack.push('a')
actual = stack.top.value
assert actual == expected