input: Write a python function to edit a solution by adding a Model-View-Controller (MVC) design pattern.
  assert edit_solution("def existing_function(): pass", "MVC").startswith("def existing_function(): pass\n class Model:\n")
  assert "class Controller:\n" in edit_solution("", "MVC")
  assert "class View:\n" in edit_solution("def another_function(): pass", "MVC")
output: def edit_solution(solution, pattern):
      if pattern != "MVC":
          return solution
  
      mvc_template = """
  class Model:
      def __init__(self):
          pass
  
  class View:
      def __init__(self):
          pass
  
  class Controller:
      def __init__(self, model, view):
          self.model = model
          self.view = view
  """
      return solution + "\n" + mvc_template