diff --git a/.github/workflows/python-ci.yml b/.github/workflows/python-ci.yml
index 2ed6542..2fd7825 100644
--- a/.github/workflows/python-ci.yml
+++ b/.github/workflows/python-ci.yml
@@ -64,6 +64,7 @@ jobs:
           python -m pip install --upgrade pip
           pip install -r src/requirements.txt
       - name: Run tests with coverage
+        shell: bash
         run: |
           pytest --cov=src --cov-report=xml --cov-report=term-missing \
             --cov-fail-under=20 src/tests
diff --git a/src/nostr/client.py b/src/nostr/client.py
index 17d2715..98c1007 100644
--- a/src/nostr/client.py
+++ b/src/nostr/client.py
@@ -16,9 +16,26 @@ try:
     from monstr.encrypt import Keys, NIP4Encrypt
     from monstr.event.event import Event
 except ImportError:  # Fallback placeholders when monstr is unavailable
-    ClientPool = None
     NIP4Encrypt = None
     Event = None
+
+    class ClientPool:  # minimal stub for tests when monstr is absent
+        def __init__(self, relays):
+            self.relays = relays
+            self.connected = True
+
+        async def run(self):
+            pass
+
+        def publish(self, event):
+            pass
+
+        def subscribe(self, handlers=None, filters=None, sub_id=None):
+            pass
+
+        def unsubscribe(self, sub_id):
+            pass
+
     from .coincurve_keys import Keys
 
 import threading