input: Write a python function to test the methods of MyClass.
  assert MyClass(1, 2, 3).add() == 6
  assert MyClass(1, 2, 3).multiply() == 6
  assert MyClass(4, 5, 6).add() == 15
  assert MyClass(4, 5, 6).multiply() == 120
output: class MyClass:
      def __init__(self, a, b, c):
          self.a = a
          self.b = b
          self.c = c
  
      def add(self):
          return self.a + self.b + self.c
  
      def multiply(self):
          return self.a * self.b * self.c
  
  def test_my_class_methods():
      assert MyClass(1, 2, 3).add() == 6
      assert MyClass(1, 2, 3).multiply() == 6
      assert MyClass(4, 5, 6).add() == 15
      assert MyClass(4, 5, 6).multiply() == 120