diff --git a/examples/atari/atari_c51.py b/examples/atari/atari_c51.py
index 98d1d08..d611ab1 100644
--- a/examples/atari/atari_c51.py
+++ b/examples/atari/atari_c51.py
@@ -174,18 +174,14 @@ def test_c51(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_dqn.py b/examples/atari/atari_dqn.py
index 7d60654..eeb9bcc 100644
--- a/examples/atari/atari_dqn.py
+++ b/examples/atari/atari_dqn.py
@@ -216,18 +216,14 @@ def main(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_fqf.py b/examples/atari/atari_fqf.py
index 185cff1..58aff46 100644
--- a/examples/atari/atari_fqf.py
+++ b/examples/atari/atari_fqf.py
@@ -187,18 +187,14 @@ def test_fqf(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_iqn.py b/examples/atari/atari_iqn.py
index 5216d7c..c609052 100644
--- a/examples/atari/atari_iqn.py
+++ b/examples/atari/atari_iqn.py
@@ -184,18 +184,14 @@ def test_iqn(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_ppo.py b/examples/atari/atari_ppo.py
index 969d00a..dd75de7 100644
--- a/examples/atari/atari_ppo.py
+++ b/examples/atari/atari_ppo.py
@@ -240,18 +240,14 @@ def test_ppo(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_qrdqn.py b/examples/atari/atari_qrdqn.py
index 5b02581..b973131 100644
--- a/examples/atari/atari_qrdqn.py
+++ b/examples/atari/atari_qrdqn.py
@@ -178,18 +178,14 @@ def test_qrdqn(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_rainbow.py b/examples/atari/atari_rainbow.py
index 5bb69a3..952d35f 100644
--- a/examples/atari/atari_rainbow.py
+++ b/examples/atari/atari_rainbow.py
@@ -214,18 +214,14 @@ def test_rainbow(args: argparse.Namespace = get_args()) -> None:
                 beta=args.beta,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/atari/atari_sac.py b/examples/atari/atari_sac.py
index be13884..4d01a88 100644
--- a/examples/atari/atari_sac.py
+++ b/examples/atari/atari_sac.py
@@ -227,18 +227,14 @@ def test_discrete_sac(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/box2d/acrobot_dualdqn.py b/examples/box2d/acrobot_dualdqn.py
index ac2c800..365c073 100644
--- a/examples/box2d/acrobot_dualdqn.py
+++ b/examples/box2d/acrobot_dualdqn.py
@@ -147,11 +147,7 @@ def test_dqn(args: argparse.Namespace = get_args()) -> None:
         policy.set_eps(args.eps_test)
         test_envs.seed(args.seed)
         test_collector.reset()
-        collector_stats = test_collector.collect(
-            n_episode=args.test_num,
-            render=args.render,
-            eval_mode=True,
-        )
+        collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
         print(collector_stats)
 
 
diff --git a/examples/box2d/bipedal_bdq.py b/examples/box2d/bipedal_bdq.py
index 7c89cd2..c817831 100644
--- a/examples/box2d/bipedal_bdq.py
+++ b/examples/box2d/bipedal_bdq.py
@@ -165,11 +165,7 @@ def test_bdq(args: argparse.Namespace = get_args()) -> None:
         policy.set_eps(args.eps_test)
         test_envs.seed(args.seed)
         test_collector.reset()
-        collector_stats = test_collector.collect(
-            n_episode=args.test_num,
-            render=args.render,
-            eval_mode=True,
-        )
+        collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
         print(collector_stats)
 
 
diff --git a/examples/box2d/bipedal_hardcore_sac.py b/examples/box2d/bipedal_hardcore_sac.py
index 2147213..66e5f31 100644
--- a/examples/box2d/bipedal_hardcore_sac.py
+++ b/examples/box2d/bipedal_hardcore_sac.py
@@ -209,11 +209,7 @@ def test_sac_bipedal(args: argparse.Namespace = get_args()) -> None:
         # Let's watch its performance!
         test_envs.seed(args.seed)
         test_collector.reset()
-        collector_stats = test_collector.collect(
-            n_episode=args.test_num,
-            render=args.render,
-            eval_mode=True,
-        )
+        collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
         print(collector_stats)
 
 
diff --git a/examples/box2d/lunarlander_dqn.py b/examples/box2d/lunarlander_dqn.py
index 8280e23..f9bbd6f 100644
--- a/examples/box2d/lunarlander_dqn.py
+++ b/examples/box2d/lunarlander_dqn.py
@@ -144,11 +144,7 @@ def test_dqn(args: argparse.Namespace = get_args()) -> None:
         policy.set_eps(args.eps_test)
         test_envs.seed(args.seed)
         test_collector.reset()
-        collector_stats = test_collector.collect(
-            n_episode=args.test_num,
-            render=args.render,
-            eval_mode=True,
-        )
+        collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
         print(collector_stats)
 
 
diff --git a/examples/box2d/mcc_sac.py b/examples/box2d/mcc_sac.py
index 97f7149..7617b7b 100644
--- a/examples/box2d/mcc_sac.py
+++ b/examples/box2d/mcc_sac.py
@@ -155,11 +155,7 @@ def test_sac(args: argparse.Namespace = get_args()) -> None:
         # Let's watch its performance!
         test_envs.seed(args.seed)
         test_collector.reset()
-        collector_stats = test_collector.collect(
-            n_episode=args.test_num,
-            render=args.render,
-            eval_mode=True,
-        )
+        collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
         print(collector_stats)
 
 
diff --git a/examples/inverse/irl_gail.py b/examples/inverse/irl_gail.py
index e30b3f6..42e5bc2 100644
--- a/examples/inverse/irl_gail.py
+++ b/examples/inverse/irl_gail.py
@@ -266,11 +266,7 @@ def test_gail(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/fetch_her_ddpg.py b/examples/mujoco/fetch_her_ddpg.py
index 8b3439a..bbf68c2 100644
--- a/examples/mujoco/fetch_her_ddpg.py
+++ b/examples/mujoco/fetch_her_ddpg.py
@@ -240,11 +240,7 @@ def test_ddpg(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     collector_stats.pprint_asdict()
 
 
diff --git a/examples/mujoco/mujoco_a2c.py b/examples/mujoco/mujoco_a2c.py
index 834e0ce..194d9b5 100755
--- a/examples/mujoco/mujoco_a2c.py
+++ b/examples/mujoco/mujoco_a2c.py
@@ -221,11 +221,7 @@ def test_a2c(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_ddpg.py b/examples/mujoco/mujoco_ddpg.py
index 066c7d4..db90bab 100755
--- a/examples/mujoco/mujoco_ddpg.py
+++ b/examples/mujoco/mujoco_ddpg.py
@@ -170,11 +170,7 @@ def test_ddpg(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_npg.py b/examples/mujoco/mujoco_npg.py
index 40cc443..4d8530a 100755
--- a/examples/mujoco/mujoco_npg.py
+++ b/examples/mujoco/mujoco_npg.py
@@ -218,11 +218,7 @@ def test_npg(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_ppo.py b/examples/mujoco/mujoco_ppo.py
index eb6817e..7c3f268 100755
--- a/examples/mujoco/mujoco_ppo.py
+++ b/examples/mujoco/mujoco_ppo.py
@@ -226,11 +226,7 @@ def test_ppo(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_redq.py b/examples/mujoco/mujoco_redq.py
index 9101f86..8951b03 100755
--- a/examples/mujoco/mujoco_redq.py
+++ b/examples/mujoco/mujoco_redq.py
@@ -198,11 +198,7 @@ def test_redq(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_reinforce.py b/examples/mujoco/mujoco_reinforce.py
index cbd4d3e..ff7e340 100755
--- a/examples/mujoco/mujoco_reinforce.py
+++ b/examples/mujoco/mujoco_reinforce.py
@@ -198,11 +198,7 @@ def test_reinforce(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_sac.py b/examples/mujoco/mujoco_sac.py
index 8d9d61e..af13983 100755
--- a/examples/mujoco/mujoco_sac.py
+++ b/examples/mujoco/mujoco_sac.py
@@ -192,11 +192,7 @@ def test_sac(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_td3.py b/examples/mujoco/mujoco_td3.py
index d1b5e69..6cc8bb2 100755
--- a/examples/mujoco/mujoco_td3.py
+++ b/examples/mujoco/mujoco_td3.py
@@ -190,11 +190,7 @@ def test_td3(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/mujoco/mujoco_trpo.py b/examples/mujoco/mujoco_trpo.py
index b5a91c0..eefdfcc 100755
--- a/examples/mujoco/mujoco_trpo.py
+++ b/examples/mujoco/mujoco_trpo.py
@@ -223,11 +223,7 @@ def test_trpo(args: argparse.Namespace = get_args()) -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/offline/atari_bcq.py b/examples/offline/atari_bcq.py
index d4e985e..3af40cc 100644
--- a/examples/offline/atari_bcq.py
+++ b/examples/offline/atari_bcq.py
@@ -191,7 +191,7 @@ def test_discrete_bcq(args: argparse.Namespace = get_args()) -> None:
         test_envs.seed(args.seed)
         print("Testing agent ...")
         test_collector.reset()
-        result = test_collector.collect(n_episode=args.test_num, render=args.render, eval_mode=True)
+        result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/offline/atari_cql.py b/examples/offline/atari_cql.py
index 69ae433..b2c0c87 100644
--- a/examples/offline/atari_cql.py
+++ b/examples/offline/atari_cql.py
@@ -175,7 +175,7 @@ def test_discrete_cql(args: argparse.Namespace = get_args()) -> None:
         test_envs.seed(args.seed)
         print("Testing agent ...")
         test_collector.reset()
-        result = test_collector.collect(n_episode=args.test_num, render=args.render, eval_mode=True)
+        result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/offline/atari_crr.py b/examples/offline/atari_crr.py
index 4e0771c..8b6320a 100644
--- a/examples/offline/atari_crr.py
+++ b/examples/offline/atari_crr.py
@@ -191,7 +191,7 @@ def test_discrete_crr(args: argparse.Namespace = get_args()) -> None:
         test_envs.seed(args.seed)
         print("Testing agent ...")
         test_collector.reset()
-        result = test_collector.collect(n_episode=args.test_num, render=args.render, eval_mode=True)
+        result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/offline/atari_il.py b/examples/offline/atari_il.py
index 928112c..39aee31 100644
--- a/examples/offline/atari_il.py
+++ b/examples/offline/atari_il.py
@@ -148,7 +148,7 @@ def test_il(args: argparse.Namespace = get_args()) -> None:
         test_envs.seed(args.seed)
         print("Testing agent ...")
         test_collector.reset()
-        result = test_collector.collect(n_episode=args.test_num, render=args.render, eval_mode=True)
+        result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/offline/d4rl_bcq.py b/examples/offline/d4rl_bcq.py
index 308a872..9ed1826 100644
--- a/examples/offline/d4rl_bcq.py
+++ b/examples/offline/d4rl_bcq.py
@@ -207,7 +207,7 @@ def test_bcq() -> None:
 
         policy.load_state_dict(torch.load(args.resume_path, map_location=torch.device("cpu")))
         collector = Collector(policy, env)
-        collector.collect(n_episode=1, render=1 / 35, eval_mode=True)
+        collector.collect(n_episode=1, render=1 / 35)
 
     if not args.watch:
         replay_buffer = load_buffer_d4rl(args.expert_data_task)
@@ -230,11 +230,7 @@ def test_bcq() -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/offline/d4rl_cql.py b/examples/offline/d4rl_cql.py
index 9d95d29..90d6b15 100644
--- a/examples/offline/d4rl_cql.py
+++ b/examples/offline/d4rl_cql.py
@@ -345,7 +345,7 @@ def test_cql() -> None:
 
         policy.load_state_dict(torch.load(args.resume_path, map_location=torch.device("cpu")))
         collector = Collector(policy, env)
-        collector.collect(n_episode=1, render=1 / 35, eval_mode=True)
+        collector.collect(n_episode=1, render=1 / 35)
 
     if not args.watch:
         replay_buffer = load_buffer_d4rl(args.expert_data_task)
@@ -368,11 +368,7 @@ def test_cql() -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/offline/d4rl_il.py b/examples/offline/d4rl_il.py
index d64cfe9..e03deed 100644
--- a/examples/offline/d4rl_il.py
+++ b/examples/offline/d4rl_il.py
@@ -143,7 +143,7 @@ def test_il() -> None:
 
         policy.load_state_dict(torch.load(args.resume_path, map_location=torch.device("cpu")))
         collector = Collector(policy, env)
-        collector.collect(n_episode=1, render=1 / 35, eval_mode=True)
+        collector.collect(n_episode=1, render=1 / 35)
 
     if not args.watch:
         replay_buffer = load_buffer_d4rl(args.expert_data_task)
@@ -166,11 +166,7 @@ def test_il() -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/offline/d4rl_td3_bc.py b/examples/offline/d4rl_td3_bc.py
index 5719eba..6b448b3 100644
--- a/examples/offline/d4rl_td3_bc.py
+++ b/examples/offline/d4rl_td3_bc.py
@@ -192,7 +192,7 @@ def test_td3_bc() -> None:
 
         policy.load_state_dict(torch.load(args.resume_path, map_location=torch.device("cpu")))
         collector = Collector(policy, env)
-        collector.collect(n_episode=1, render=1 / 35, eval_mode=True)
+        collector.collect(n_episode=1, render=1 / 35)
 
     if not args.watch:
         replay_buffer = load_buffer_d4rl(args.expert_data_task)
@@ -218,11 +218,7 @@ def test_td3_bc() -> None:
     # Let's watch its performance!
     test_envs.seed(args.seed)
     test_collector.reset()
-    collector_stats = test_collector.collect(
-        n_episode=args.test_num,
-        render=args.render,
-        eval_mode=True,
-    )
+    collector_stats = test_collector.collect(n_episode=args.test_num, render=args.render)
     print(collector_stats)
 
 
diff --git a/examples/vizdoom/vizdoom_c51.py b/examples/vizdoom/vizdoom_c51.py
index 8a52e5f..25ad804 100644
--- a/examples/vizdoom/vizdoom_c51.py
+++ b/examples/vizdoom/vizdoom_c51.py
@@ -180,18 +180,14 @@ def test_c51(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/examples/vizdoom/vizdoom_ppo.py b/examples/vizdoom/vizdoom_ppo.py
index adbfb05..7fc09f6 100644
--- a/examples/vizdoom/vizdoom_ppo.py
+++ b/examples/vizdoom/vizdoom_ppo.py
@@ -242,18 +242,14 @@ def test_ppo(args: argparse.Namespace = get_args()) -> None:
                 stack_num=args.frames_stack,
             )
             collector = Collector(policy, test_envs, buffer, exploration_noise=True)
-            result = collector.collect(n_step=args.buffer_size, eval_mode=True)
+            result = collector.collect(n_step=args.buffer_size)
             print(f"Save buffer into {args.save_buffer_name}")
             # Unfortunately, pickle will cause oom with 1M buffer size
             buffer.save_hdf5(args.save_buffer_name)
         else:
             print("Testing agent ...")
             test_collector.reset()
-            result = test_collector.collect(
-                n_episode=args.test_num,
-                render=args.render,
-                eval_mode=True,
-            )
+            result = test_collector.collect(n_episode=args.test_num, render=args.render)
         result.pprint_asdict()
 
     if args.watch:
diff --git a/test/base/test_env_finite.py b/test/base/test_env_finite.py
index ce8a936..35bf3e2 100644
--- a/test/base/test_env_finite.py
+++ b/test/base/test_env_finite.py
@@ -250,7 +250,7 @@ def test_finite_dummy_vector_env() -> None:
         envs.tracker = MetricTracker()
         try:
             # TODO: why on earth 10**18?
-            test_collector.collect(n_step=10**18)
+            test_collector.collect(n_step=10 ** 18)
         except StopIteration:
             envs.tracker.validate()
 
@@ -265,6 +265,6 @@ def test_finite_subproc_vector_env() -> None:
     for _ in range(3):
         envs.tracker = MetricTracker()
         try:
-            test_collector.collect(n_step=10**18)
+            test_collector.collect(n_step=10 ** 18)
         except StopIteration:
             envs.tracker.validate()
diff --git a/test/base/test_policy.py b/test/base/test_policy.py
index f286156..4d26905 100644
--- a/test/base/test_policy.py
+++ b/test/base/test_policy.py
@@ -64,7 +64,7 @@ def policy(request: pytest.FixtureRequest) -> PPOPolicy:
 
 class TestPolicyBasics:
     def test_get_action(self, policy: PPOPolicy) -> None:
-        policy.is_eval = True
+        policy.is_within_training_step = False
         sample_obs = torch.randn(obs_shape)
         policy.deterministic_eval = False
         actions = [policy.compute_action(sample_obs) for _ in range(10)]
diff --git a/test/offline/gather_cartpole_data.py b/test/offline/gather_cartpole_data.py
index 7d6aba1..19ba653 100644
--- a/test/offline/gather_cartpole_data.py
+++ b/test/offline/gather_cartpole_data.py
@@ -167,7 +167,7 @@ def gather_data() -> VectorReplayBuffer | PrioritizedVectorReplayBuffer:
     policy.set_eps(0.2)
     collector = Collector(policy, test_envs, buf, exploration_noise=True)
     collector.reset()
-    collector_stats = collector.collect(n_step=args.buffer_size, eval_mode=True)
+    collector_stats = collector.collect(n_step=args.buffer_size)
     if args.save_buffer_name.endswith(".hdf5"):
         buf.save_hdf5(args.save_buffer_name)
     else:
diff --git a/test/offline/test_bcq.py b/test/offline/test_bcq.py
index 20e4dd6..8b31c19 100644
--- a/test/offline/test_bcq.py
+++ b/test/offline/test_bcq.py
@@ -185,7 +185,7 @@ def test_bcq(args: argparse.Namespace = get_args()) -> None:
             torch.load(os.path.join(log_path, "policy.pth"), map_location=torch.device("cpu")),
         )
         collector = Collector(policy, env)
-        collector.collect(n_episode=1, render=1 / 35, eval_mode=True)
+        collector.collect(n_episode=1, render=1 / 35)
 
     # trainer
     result = OfflineTrainer(
diff --git a/test/pettingzoo/pistonball.py b/test/pettingzoo/pistonball.py
index 27392f7..c57522d 100644
--- a/test/pettingzoo/pistonball.py
+++ b/test/pettingzoo/pistonball.py
@@ -190,5 +190,5 @@ def watch(args: argparse.Namespace = get_args(), policy: BasePolicy | None = Non
         policy, _, _ = get_agents(args)
     [agent.set_eps(args.eps_test) for agent in policy.policies.values()]
     collector = Collector(policy, env, exploration_noise=True)
-    result = collector.collect(n_episode=1, render=args.render, eval_mode=True)
+    result = collector.collect(n_episode=1, render=args.render)
     result.pprint_asdict()
diff --git a/test/pettingzoo/pistonball_continuous.py b/test/pettingzoo/pistonball_continuous.py
index ed08522..38de811 100644
--- a/test/pettingzoo/pistonball_continuous.py
+++ b/test/pettingzoo/pistonball_continuous.py
@@ -285,5 +285,5 @@ def watch(args: argparse.Namespace = get_args(), policy: BasePolicy | None = Non
         )
         policy, _, _ = get_agents(args)
     collector = Collector(policy, env)
-    collector_result = collector.collect(n_episode=1, render=args.render, eval_mode=True)
+    collector_result = collector.collect(n_episode=1, render=args.render)
     collector_result.pprint_asdict()
diff --git a/test/pettingzoo/tic_tac_toe.py b/test/pettingzoo/tic_tac_toe.py
index fc46e2a..966c9e0 100644
--- a/test/pettingzoo/tic_tac_toe.py
+++ b/test/pettingzoo/tic_tac_toe.py
@@ -230,5 +230,5 @@ def watch(
     policy, optim, agents = get_agents(args, agent_learn=agent_learn, agent_opponent=agent_opponent)
     policy.policies[agents[args.agent_id - 1]].set_eps(args.eps_test)
     collector = Collector(policy, env, exploration_noise=True)
-    result = collector.collect(n_episode=1, render=args.render, eval_mode=True)
+    result = collector.collect(n_episode=1, render=args.render)
     result.pprint_asdict()
diff --git a/tianshou/data/collector.py b/tianshou/data/collector.py
index 10cf663..cf897a5 100644
--- a/tianshou/data/collector.py
+++ b/tianshou/data/collector.py
@@ -260,17 +260,8 @@ class BaseCollector(ABC):
     ) -> CollectStats:
         pass
 
-    def collect(
-        self,
-        n_step: int | None = None,
-        n_episode: int | None = None,
-        random: bool = False,
-        render: float | None = None,
-        no_grad: bool = True,
-        reset_before_collect: bool = False,
-        gym_reset_kwargs: dict[str, Any] | None = None,
-        eval_mode: bool = False,
-    ) -> CollectStats:
+    def collect(self, n_step: int | None = None, n_episode: int | None = None, random: bool = False, render: float | None = None,
+            no_grad: bool = True, reset_before_collect: bool = False, gym_reset_kwargs: dict[str, Any] | None = None) -> CollectStats:
         """Collect a specified number of steps or episodes.
 
         To ensure an unbiased sampling result with the n_episode option, this function will
@@ -286,9 +277,6 @@ class BaseCollector(ABC):
             (The collector needs the initial obs and info to function properly.)
         :param gym_reset_kwargs: extra keyword arguments to pass into the environment's
             reset function. Only used if reset_before_collect is True.
-        :param eval_mode: whether to collect data in evaluation mode. Will
-            set the policy to training mode otherwise.
-
         .. note::
 
             One and only one collection number specification is permitted, either
@@ -302,8 +290,7 @@ class BaseCollector(ABC):
         if reset_before_collect:
             self.reset(reset_buffer=False, gym_reset_kwargs=gym_reset_kwargs)
 
-        policy_mode_context = in_eval_mode if eval_mode else in_train_mode
-        with policy_mode_context(self.policy):
+        with in_eval_mode(self.policy):  # safety precaution only
             return self._collect(
                 n_step=n_step,
                 n_episode=n_episode,
diff --git a/tianshou/highlevel/agent.py b/tianshou/highlevel/agent.py
index c131326..fdfc4c0 100644
--- a/tianshou/highlevel/agent.py
+++ b/tianshou/highlevel/agent.py
@@ -130,10 +130,7 @@ class AgentFactory(ABC, ToStringMixin):
             log.info(
                 f"Collecting {self.sampling_config.start_timesteps} initial environment steps before training (random={self.sampling_config.start_timesteps_random})",
             )
-            train_collector.collect(
-                n_step=self.sampling_config.start_timesteps,
-                random=self.sampling_config.start_timesteps_random,
-            )
+            train_collector.collect(n_step=self.sampling_config.start_timesteps, random=self.sampling_config.start_timesteps_random)
         return train_collector, test_collector
 
     def set_policy_wrapper_factory(
diff --git a/tianshou/highlevel/experiment.py b/tianshou/highlevel/experiment.py
index df87aca..e7ccc9f 100644
--- a/tianshou/highlevel/experiment.py
+++ b/tianshou/highlevel/experiment.py
@@ -337,7 +337,7 @@ class Experiment(ToStringMixin):
     ) -> None:
         collector = Collector(policy, env)
         collector.reset()
-        result = collector.collect(n_episode=num_episodes, render=render, eval_mode=True)
+        result = collector.collect(n_episode=num_episodes, render=render)
         assert result.returns_stat is not None  # for mypy
         assert result.lens_stat is not None  # for mypy
         log.info(
diff --git a/tianshou/policy/base.py b/tianshou/policy/base.py
index e566d0c..498a333 100644
--- a/tianshou/policy/base.py
+++ b/tianshou/policy/base.py
@@ -226,8 +226,18 @@ class BasePolicy(nn.Module, Generic[TTrainingStats], ABC):
         self.action_scaling = action_scaling
         self.action_bound_method = action_bound_method
         self.lr_scheduler = lr_scheduler
-        # whether the policy is in evaluation mode
-        self.is_eval = False  # TODO: remove in favor of kwarg in compute_action/forward?
+        self.is_within_training_step = False
+        """
+        flag indicating whether we are currently within a training step, which encompasses data collection
+        for training and the policy update (gradient steps).
+        
+        It can be used, for example, to control whether a flag controlling deterministic evaluation should 
+        indeed be applied, because within a training step, we typically always want to apply stochastic evaluation
+        (even if such a flag is enabled). 
+        
+        This flag should normally remain False and should be set to True only by the algorithm which performs
+        training steps.
+        """
         self._compile()
 
     @property
diff --git a/tianshou/policy/modelfree/discrete_sac.py b/tianshou/policy/modelfree/discrete_sac.py
index 7e731b1..8c79428 100644
--- a/tianshou/policy/modelfree/discrete_sac.py
+++ b/tianshou/policy/modelfree/discrete_sac.py
@@ -107,7 +107,7 @@ class DiscreteSACPolicy(SACPolicy[TDiscreteSACTrainingStats]):
     ) -> Batch:
         logits_BA, hidden_BH = self.actor(batch.obs, state=state, info=batch.info)
         dist = Categorical(logits=logits_BA)
-        act_B = dist.mode if self.deterministic_eval and self.is_eval else dist.sample()
+        act_B = dist.mode if self.deterministic_eval and not self.is_within_training_step else dist.sample()
         return Batch(logits=logits_BA, act=act_B, state=hidden_BH, dist=dist)
 
     def _target_q(self, buffer: ReplayBuffer, indices: np.ndarray) -> torch.Tensor:
diff --git a/tianshou/policy/modelfree/pg.py b/tianshou/policy/modelfree/pg.py
index 4792db8..3ef82be 100644
--- a/tianshou/policy/modelfree/pg.py
+++ b/tianshou/policy/modelfree/pg.py
@@ -197,7 +197,7 @@ class PGPolicy(BasePolicy[TPGTrainingStats], Generic[TPGTrainingStats]):
         # the action_dist_input_BD in that case is a tuple of loc_B, scale_B and needs to be unpacked
         dist = self.dist_fn(action_dist_input_BD)
 
-        act_B = dist.mode if self.deterministic_eval and self.is_eval else dist.sample()
+        act_B = dist.mode if self.deterministic_eval and not self.is_within_training_step else dist.sample()
         # act is of dimension BA in continuous case and of dimension B in discrete
         result = Batch(logits=action_dist_input_BD, act=act_B, state=hidden_BH, dist=dist)
         return cast(DistBatchProtocol, result)
diff --git a/tianshou/policy/modelfree/redq.py b/tianshou/policy/modelfree/redq.py
index a216cf9..25f2997 100644
--- a/tianshou/policy/modelfree/redq.py
+++ b/tianshou/policy/modelfree/redq.py
@@ -153,7 +153,7 @@ class REDQPolicy(DDPGPolicy[TREDQTrainingStats]):
     ) -> Batch:
         (loc_B, scale_B), h_BH = self.actor(batch.obs, state=state, info=batch.info)
         dist = Independent(Normal(loc_B, scale_B), 1)
-        if self.deterministic_eval and self.is_eval:
+        if self.deterministic_eval and not self.is_within_training_step:
             act_B = dist.mode
         else:
             act_B = dist.rsample()
diff --git a/tianshou/policy/modelfree/sac.py b/tianshou/policy/modelfree/sac.py
index 3dbea75..a5a05c0 100644
--- a/tianshou/policy/modelfree/sac.py
+++ b/tianshou/policy/modelfree/sac.py
@@ -175,7 +175,7 @@ class SACPolicy(DDPGPolicy[TSACTrainingStats], Generic[TSACTrainingStats]):  # t
     ) -> DistLogProbBatchProtocol:
         (loc_B, scale_B), hidden_BH = self.actor(batch.obs, state=state, info=batch.info)
         dist = Independent(Normal(loc=loc_B, scale=scale_B), 1)
-        if self.deterministic_eval and self.is_eval:
+        if self.deterministic_eval and not self.is_within_training_step:
             act_B = dist.mode
         else:
             act_B = dist.rsample()
diff --git a/tianshou/trainer/base.py b/tianshou/trainer/base.py
index 825c80c..213da7b 100644
--- a/tianshou/trainer/base.py
+++ b/tianshou/trainer/base.py
@@ -3,6 +3,7 @@ import time
 from abc import ABC, abstractmethod
 from collections import defaultdict, deque
 from collections.abc import Callable
+from contextlib import contextmanager
 from dataclasses import asdict
 from typing import Optional, Tuple
 
@@ -407,23 +408,34 @@ class BaseTrainer(ABC):
 
         return test_stat, stop_fn_flag
 
+    @contextmanager
+    def _is_within_training_step_enabled(self, is_within_training_step: bool):
+        old_value = self.policy.is_within_training_step
+        try:
+            self.policy.is_within_training_step = is_within_training_step
+            yield
+        finally:
+            self.policy.is_within_training_step = old_value
+
     def training_step(self) -> Tuple[CollectStatsBase, Optional[TrainingStats], bool]:
-        should_stop_training = False
+        with self._is_within_training_step_enabled(True):
 
-        if self.train_collector is not None:
-            collect_stats = self._collect_training_data()
-            should_stop_training = self._test_in_train(collect_stats)
-        else:
-            collect_stats = CollectStatsBase(
-                n_collected_episodes=len(self.buffer),
-            )
+            should_stop_training = False
 
-        if not should_stop_training:
-            training_stats = self.policy_update_fn(collect_stats)
-        else:
-            training_stats = None
+            if self.train_collector is not None:
+                collect_stats = self._collect_training_data()
+                should_stop_training = self._test_in_train(collect_stats)
+            else:
+                collect_stats = CollectStatsBase(
+                    n_collected_episodes=len(self.buffer),
+                )
 
-        return collect_stats, training_stats, should_stop_training
+            if not should_stop_training:
+                training_stats = self.policy_update_fn(collect_stats)
+            else:
+                training_stats = None
+
+            return collect_stats, training_stats, should_stop_training
 
     def _collect_training_data(self) -> CollectStats:
         """Performs training data collection
@@ -434,10 +446,7 @@ class BaseTrainer(ABC):
         assert self.train_collector is not None
         if self.train_fn:
             self.train_fn(self.epoch, self.env_step)
-        collect_stats = self.train_collector.collect(
-            n_step=self.step_per_collect,
-            n_episode=self.episode_per_collect,
-        )
+        collect_stats = self.train_collector.collect(n_step=self.step_per_collect, n_episode=self.episode_per_collect)
 
         self.env_step += collect_stats.n_collected_steps
 
@@ -467,26 +476,28 @@ class BaseTrainer(ABC):
         """
         should_stop_training = False
 
-        if (
-            collect_stats.n_collected_episodes > 0
-            and self.test_in_train
-            and self.stop_fn
-            and self.stop_fn(collect_stats.returns_stat.mean)  # type: ignore
-        ):
-            assert self.test_collector is not None
-            test_result = test_episode(
-                self.test_collector,
-                self.test_fn,
-                self.epoch,
-                self.episode_per_test,
-                self.logger,
-                self.env_step,
-            )
-            assert test_result.returns_stat is not None  # for mypy
-            if self.stop_fn(test_result.returns_stat.mean):
-                should_stop_training = True
-                self.best_reward = test_result.returns_stat.mean
-                self.best_reward_std = test_result.returns_stat.std
+        # Because we need to evaluate the policy, we need to temporarily leave the "is_training_step" semantics
+        with self._is_within_training_step_enabled(False):
+            if (
+                collect_stats.n_collected_episodes > 0
+                and self.test_in_train
+                and self.stop_fn
+                and self.stop_fn(collect_stats.returns_stat.mean)  # type: ignore
+            ):
+                assert self.test_collector is not None
+                test_result = test_episode(
+                    self.test_collector,
+                    self.test_fn,
+                    self.epoch,
+                    self.episode_per_test,
+                    self.logger,
+                    self.env_step,
+                )
+                assert test_result.returns_stat is not None  # for mypy
+                if self.stop_fn(test_result.returns_stat.mean):
+                    should_stop_training = True
+                    self.best_reward = test_result.returns_stat.mean
+                    self.best_reward_std = test_result.returns_stat.std
 
         return should_stop_training
 
diff --git a/tianshou/trainer/utils.py b/tianshou/trainer/utils.py
index 0c2bf18..767e76d 100644
--- a/tianshou/trainer/utils.py
+++ b/tianshou/trainer/utils.py
@@ -27,7 +27,7 @@ def test_episode(
     collector.reset(reset_stats=False)
     if test_fn:
         test_fn(epoch, global_step)
-    result = collector.collect(n_episode=n_episode, eval_mode=True)
+    result = collector.collect(n_episode=n_episode)
     if reward_metric:  # TODO: move into collector
         rew = reward_metric(result.returns)
         result.returns = rew