input: Write a function to create a class in Python that implements two methods for adding two numbers. The first method should accept two numbers and return their sum, and the second method should accept three numbers and return their sum. If the class is implemented correctly, a test case should assert that the result of adding two numbers equals 3, and another test case should assert that the result of adding three numbers equals 6.
  
  class Calculator:
   def __init__(self):
     pass
      
   def add_two_numbers(self, a, b):
     return a + b
  
   def add(self, a, b, c):
     return a + b + c
  
  assert Calculator().add_two_numbers(1, 2) == 3
  assert Calculator().add(1, 2, 3) == 6
output: 
  class Calculator:
   def __init__(self):
     pass
      
   def add_two_numbers(self, a, b):
     return a + b
  
   def add(self, a, b, c):
     return a + b + c
  