Add tests for this behavior

Author: Jonathan Harper

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

@@ -12,6 +12,7 @@
 from mlagents.trainers.env_manager import EnvironmentStep
 from mlagents_envs.base_env import BaseEnv
 from mlagents_envs.side_channel.engine_configuration_channel import EngineConfig
+from mlagents_envs.exception import UnityEnvironmentException
 from mlagents.trainers.tests.simple_test_envs import SimpleEnvironment
 from mlagents.trainers.stats import StatsReporter
 from mlagents.trainers.tests.test_simple_rl import (
@@ -168,13 +169,12 @@ def test_advance(self, mock_create_worker, external_brains_mock, step_mock):
         assert agent_manager_mock.policy == mock_policy
 
 
-def simple_env_factory(worker_id, config):
-    env = SimpleEnvironment(["1D"], use_discrete=True)
-    return env
-
-
 @pytest.mark.parametrize("num_envs", [1, 4])
 def test_subprocess_env_endtoend(num_envs):
+    def simple_env_factory(worker_id, config):
+        env = SimpleEnvironment(["1D"], use_discrete=True)
+        return env
+
     env_manager = SubprocessEnvManager(
         simple_env_factory, EngineConfig.default_config(), num_envs
     )
@@ -193,3 +193,22 @@ def test_subprocess_env_endtoend(num_envs):
         val > 0.7 for val in StatsReporter.writers[0].get_last_rewards().values()
     )
     env_manager.close()
+
+
+@pytest.mark.parametrize("num_envs", [1, 4])
+def test_subprocess_env_raises_errors(num_envs):
+    def failing_env_factory(worker_id, config):
+        import time
+
+        # Sleep momentarily to allow time for the EnvManager to be waiting for the
+        # subprocess response.  We won't be able to capture failures from the subprocess
+        # that cause it to close the pipe before we can send the first message.
+        time.sleep(0.1)
+        raise UnityEnvironmentException()
+
+    env_manager = SubprocessEnvManager(
+        failing_env_factory, EngineConfig.default_config(), num_envs
+    )
+    with pytest.raises(UnityEnvironmentException):
+        env_manager.reset()
+    env_manager.close()