input: Write a python function to implement a stack class with methods to check if it is empty, push an item, pop an item, peek the top item, and get its size.
  assert stack.isEmpty() == True
  stack.push(1)
  assert stack.isEmpty() == False
  assert stack.peek() == 1
  stack.push(2)
  assert stack.size() == 2
  assert stack.pop() == 2
  assert stack.size() == 1
output: 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()
          else:
              raise IndexError("pop from empty stack")
  
      def peek(self):
          if not self.isEmpty():
              return self.items[-1]
          else:
              raise IndexError("peek from empty stack")
  
      def size(self):
          return len(self.items)
  
  # Testing the stack class with given assertions
  stack = Stack()
  assert stack.isEmpty() == True
  stack.push(1)
  assert stack.isEmpty() == False
  assert stack.peek() == 1
  stack.push(2)
  assert stack.size() == 2
  assert stack.pop() == 2
  assert stack.size() == 1