input: Write a function to implement a chatbot in Python that can provide customer support in a restaurant. The function should take a file name as input and read the user's question from the file. Based on the question, the chatbot will randomly select and display an appropriate response from a list of pre-defined responses.
  
  assert restaurant_chatbot('random_user_question.txt')=='We serve a variety of dishes - from salads to pizzas to steaks!'
  assert restaurant_chatbot('another_user_question.txt')=='Check out our menu for a full list of options'
  assert restaurant_chatbot('some_user_question.txt')=="We have a unique selection of meals - have you checked out our menu?"
  assert restaurant_chatbot('no_question.txt')=='We have a great selection of meals! What kind of dish are you looking for?'
  assert restaurant_chatbot('empty_question.txt')=='We serve a variety of dishes, including traditional Italian, Mexican, and American fare. What would you like to try?'
output: import random
  
  def restaurant_chatbot(file_name):
      responses = {
          "menu": ["Check out our menu for a full list of options", "We have a unique selection of meals - have you checked out our menu?"],
          "dishes": ["We serve a variety of dishes - from salads to pizzas to steaks!", "We have a great selection of meals! What kind of dish are you looking for?"],
          "default": ["We serve a variety of dishes, including traditional Italian, Mexican, and American fare. What would you like to try?"]
      }
      
      try:
          with open(file_name, 'r') as file:
              question = file.read().strip().lower()
              if "menu" in question:
                  return random.choice(responses["menu"])
              elif "dish" in question or "dishes" in question:
                  return random.choice(responses["dishes"])
              else:
                  return random.choice(responses["default"])
      except FileNotFoundError:
          return random.choice(responses["default"])