Add 2 visual obs test

ml-agents/mlagents/trainers/tests/test_rl_trainer.py

 
 @mock.patch("mlagents.trainers.rl_trainer.RLTrainer.add_policy_outputs")
 @mock.patch("mlagents.trainers.rl_trainer.RLTrainer.add_rewards_outputs")
-@pytest.mark.parametrize("num_vis_obs", [0, 1], ids=["", "viz"])
+@pytest.mark.parametrize("num_vis_obs", [0, 1, 2], ids=["vec", "1 viz", "2 viz"])
 def test_rl_trainer(add_policy_outputs, add_rewards_outputs, num_vis_obs):
     trainer = create_rl_trainer()
     trainer.policy = create_mock_policy()