def test_stack_peek(self):
stack = Stack()
stack.push(77)
stack.push(123)
self.assertEqual(stack.peek(), 123, "We should peek 123")
self.assertEqual(stack.pop(), 123, "We hsould pop 123")
self.assertEqual(stack.peek(), 77, "We should peek 77")
self.assertEqual(stack.pop(), 77, "We should pop 77")
self.assertEqual(stack.size(), 0)
self.assertIsNone(stack.peek(), "peek is none")
def test_pop_two_element(self):
stack = Stack()
stack.push(1)
stack.push(2)
self.assertEqual(stack.pop(), 2, "We should pop 2")
self.assertEqual(stack.peek(), 1)
self.assertEqual(stack.size(), 1)
self.assertEqual(stack.pop(), 1, "We should pop 1")
self.assertEqual(stack.size(), 0)
def test_peek_empty(self):
stack = Stack()
self.assertIsNone(stack.peek(), "peek is none")