def test__stack_operations__ok(self):
s = Stack()
s.push(10)
assert s.size() == 1
assert s.peek() == 10
s.push(22)
assert s.size() == 2
assert s.peek() == 22
assert s.is_empty() == False
s.pop()
assert s.size() == 1
s.pop()
assert s.size() == 0
assert s.is_empty() == True
def test__new_stack__is_empty(self):
s = Stack()
assert s.size() == 0
assert s.is_empty() == True
assert s.peek() == None
