input: Write a function to create a Python class named Calculator that implements two methods to add two numbers. The class should have a constructor and two methods: one to add two numbers and another to add three numbers. Additionally, provide assert statements for testing the functionality of the methods.
  class Calculator:
   def __init__(self):
     pass
      
   def add_two_numbers(self, a, b):
     return a + b
  
   def add_three_numbers(self, a, b, c):
     return a + b + c
  
  assert Calculator().add_two_numbers(1, 2) == 3
  assert Calculator().add_three_numbers(1, 2, 3) == 6
output: class Calculator:
   def __init__(self):
     pass
      
   def add_two_numbers(self, a, b):
     return a + b
  
   def add_three_numbers(self, a, b, c):
     return a + b + c