input: Write a python function to test the functionality of a Stack class.
  assert my_stack.isEmpty() == True
  my_stack.push(1)
  my_stack.push(2)
  assert my_stack.peek() == 2
  assert my_stack.size() == 2
  assert my_stack.pop() == 2
  assert my_stack.size() == 1
  assert my_stack.isEmpty() == False
output: def test_stack():
      class Stack:
          def __init__(self):
              self.items = []
  
          def isEmpty(self):
              return len(self.items) == 0
  
          def push(self, item):
              self.items.append(item)
  
          def pop(self):
              if not self.isEmpty():
                  return self.items.pop()
  
          def peek(self):
              if not self.isEmpty():
                  return self.items[-1]
  
          def size(self):
              return len(self.items)
  
      my_stack = Stack()
  
      assert my_stack.isEmpty() == True
      my_stack.push(1)
      my_stack.push(2)
      assert my_stack.peek() == 2
      assert my_stack.size() == 2
      assert my_stack.pop() == 2
      assert my_stack.size() == 1
      assert my_stack.isEmpty() == False