fix handling of kernel activity

jupyter_server/services/kernels/kernelmanager.py

@@ -527,7 +527,7 @@ def record_activity(msg_list):
     def stop_watching_activity(self, kernel_id):
         """Stop watching IOPub messages on a kernel for activity."""
         kernel = self._kernels[kernel_id]
-        if kernel._activity_stream:
+        if getattr(kernel, '_activity_stream', None):
             kernel._activity_stream.close()
             kernel._activity_stream = None
 

jupyter_server/tests/services/sessions/test_api.py

@@ -1,4 +1,5 @@
 import json
+import os
 import shutil
 import time
 
@@ -246,7 +247,8 @@ async def test_create_bad_pending(
     resp = await session_client.list()
     session = j(resp)[0]
     assert session["kernel"]["execution_state"] == "dead"
-    assert "non_existent_path" in session["kernel"]["reason"]
+    if os.name != "nt":
+        assert "non_existent_path" in session["kernel"]["reason"]
 
     # Need to find a better solution to this.
     await session_client.cleanup()