diff --git a/qns/entity/cchannel/cchannel_ex.py b/qns/entity/cchannel/cchannel_ex.py
index b1c5e01..cc4bd9c 100644
--- a/qns/entity/cchannel/cchannel_ex.py
+++ b/qns/entity/cchannel/cchannel_ex.py
@@ -15,13 +15,15 @@
 #    You should have received a copy of the GNU General Public License
 #    along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-from typing import Any, List
+from typing import List, Union
 
 from qns.simulator.ts import Time
 from qns.entity.node.node import QNode
 from qns.models.delay.delay import DelayModel
 from qns.simulator.simulator import Simulator
-from qns.entity.cchannel.cchannel import *
+from qns.utils.rnd import get_rand
+import qns.utils.log as log
+from qns.entity.cchannel.cchannel import ClassicPacket, ClassicChannel, RecvClassicPacket, NextHopNotConnectionException
 
 
 class ClassicChannelEx(ClassicChannel):
@@ -35,8 +37,8 @@ def __init__(
         name: str = None,
         node_list: List[QNode] = [],
         bandwidth: int = 0,
-        delay: float | DelayModel = 0,
-        length: float | None = 0,
+        delay: Union[float, DelayModel] = 0,
+        length: Union[float, None] = 0,
         drop_rate: float = 0,
         max_buffer_size: int = 0,
     ):
diff --git a/qns/simulator/stablepool.py b/qns/simulator/stablepool.py
index 9f0e586..0e845fb 100644
--- a/qns/simulator/stablepool.py
+++ b/qns/simulator/stablepool.py
@@ -30,7 +30,7 @@ def __eq__(self, other) -> bool:
             return self.event == other.event and self.seq == other.seq
 
         def __lt__(self, other) -> bool:
-            return self.event < other.event or (@
+            return self.event < other.event or (
                 self.event == other.event and self.seq < other.seq
             )
 
diff --git a/test/entity/test_cchannelex.py b/test/entity/test_cchannelex.py
index f2ad33d..a8a1154 100644
--- a/test/entity/test_cchannelex.py
+++ b/test/entity/test_cchannelex.py
@@ -1,8 +1,10 @@
 from qns.simulator.event import Event
 from qns.simulator import Simulator, func_to_event
-from qns.utils.log import *
 from qns.simulator.stablepool import StableEventPool
-from qns.entity import *
+from qns.entity.node.node import QNode
+from qns.entity.node.app import Application
+from qns.utils.log import install
+from qns.entity.cchannel.cchannel import ClassicChannel, ClassicPacket
 from qns.entity.cchannel.cchannel_ex import ClassicChannelEx
 
 
@@ -48,16 +50,14 @@ def recv(self, node, event: Event):
         self.recved_time.append(self._simulator.tc)
 
 
-def test(ex, tparam):
+def _run_sim(is_used, tparam):
     sim = Simulator(0, 10, pool_cls=StableEventPool)
-
     install(sim)
 
     n1 = QNode("n1")
     n2 = QNode("n2")
 
-    global c12
-    if not ex:
+    if not is_used:
         c12 = ClassicChannel(
             bandwidth=tparam[0],
             drop_rate=tparam[1],
@@ -94,27 +94,30 @@ def test(ex, tparam):
 
     s1.start()
     s2.start()
-
     sim.run()
 
-    print(f"n1->n2: {r1.recved}")
-    print(f"time:{r1.recved_time}")
-    print(f"\nn2->n1: {r2.recved}")
-    print(f"time:{r2.recved_time}")
-
-
-bidir = (2, 0, 0, 1)
-print("============================")
-print("bidir w/o Ex:")
-test(False, bidir)
-print("---------------")
-print("bidir w/ Ex:")
-test(True, bidir)
-
-reliable = (0, 0.5, 1, 0)
-print("============================")
-print("reliable w/o Ex:")
-test(False, reliable)
-print("---------------")
-print("reliable w/ Ex:")
-test(True, reliable)
+    print(f"\nn1->n2: {r1.recved}, time: {r1.recved_time}")
+    print(f"n2->n1: {r2.recved}, time: {r2.recved_time}")
+
+
+def test_bidir_without_ex():
+    print("\n--- bidir w/o Ex ---")
+    _run_sim(False, (2, 0, 0, 1))
+
+def test_bidir_with_ex():
+    print("\n--- bidir w/ Ex ---")
+    _run_sim(True, (2, 0, 0, 1))
+
+def test_reliable_without_ex():
+    print("\n--- reliable w/o Ex ---")
+    _run_sim(False, (0, 0.5, 1, 0))
+
+def test_reliable_with_ex():
+    print("\n--- reliable w/ Ex ---")
+    _run_sim(True, (0, 0.5, 1, 0))
+
+
+test_bidir_without_ex()
+test_bidir_with_ex()
+test_reliable_without_ex()
+test_reliable_with_ex()
\ No newline at end of file