code: def compare_agents(EnvFactory, AgentFactories, n=10, steps=1000):
      
      envs = [EnvFactory() for i in range(n)]
      return [(A, test_agent(A, steps, copy.deepcopy(envs)))
              for A in AgentFactories]
docs: See how well each of several agents do in n instances of an environment.
      Pass in a factory (constructor) for environments, and several for agents.
      Create n instances of the environment, and run each agent in copies of
      each one for steps. Return a list of (agent, average-score) tuples.