input: Write a python function to generate a random user agent string using the given Provider class.
  assert 'Mozilla/5.0' in Provider.user_agent()
  assert any(agent in Provider.user_agent() for agent in Provider.user_agents)
  assert isinstance(Provider.user_agent(), str)
output: import random
  
  class Provider:
      user_agents = [
          'Mozilla/5.0 (Windows NT 10.0; Win64; x64)',
          'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)',
          'Mozilla/5.0 (X11; Linux x86_64)',
          'Mozilla/5.0 (iPhone; CPU iPhone OS 14_0 like Mac OS X)',
          'Mozilla/5.0 (iPad; CPU OS 14_0 like Mac OS X)'
      ]
  
      @staticmethod
      def user_agent():
          return random.choice(Provider.user_agents)