Fix discrete CarRacing-v3 (#1253)

Co-authored-by: Mark Towers <[email protected]>

gymnasium/envs/box2d/car_racing.py

@@ -541,8 +541,8 @@ def reset(
     def step(self, action: Union[np.ndarray, int]):
         assert self.car is not None
         if action is not None:
-            action = action.astype(np.float64)
             if self.continuous:
+                action = action.astype(np.float64)
                 self.car.steer(-action[0])
                 self.car.gas(action[1])
                 self.car.brake(action[2])

tests/envs/test_env_implementation.py

@@ -8,6 +8,7 @@
 from gymnasium.envs.box2d.lunar_lander import demo_heuristic_lander
 from gymnasium.envs.toy_text import CliffWalkingEnv, TaxiEnv
 from gymnasium.envs.toy_text.frozen_lake import generate_random_map
+from gymnasium.error import InvalidAction
 
 
 def test_lunar_lander_heuristics():
@@ -343,3 +344,24 @@ def test_cartpole_vector_equiv():
 
     env.close()
     envs.close()
+
+
+@pytest.mark.parametrize("env_id", ["CarRacing-v3", "LunarLander-v3"])
+def test_discrete_action_validation(env_id):
+    # get continuous action
+    continuous_env = gym.make(env_id, continuous=True)
+    continuous_action = continuous_env.action_space.sample()
+    continuous_env.close()
+
+    # create discrete env
+    discrete_env = gym.make(env_id, continuous=False)
+    discrete_env.reset()
+
+    # expect InvalidAction (caused by CarRacing) or AssertionError (caused by LunarLander)
+    with pytest.raises((InvalidAction, AssertionError)):
+        discrete_env.step(continuous_action)
+
+    # expect no error
+    discrete_action = discrete_env.action_space.sample()
+    discrete_env.step(discrete_action)
+    discrete_env.close()