Test downstream projects

.github/workflows/downstream.yml

@@ -0,0 +1,32 @@
+name: Test downstream projects
+
+on:
+  push:
+    branches: "*"
+  pull_request:
+    branches: "*"
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Set up Python 3.9
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+
+      - name: Install dependencies
+        run: |
+          pip install --upgrade pip
+          pip install .
+          pip install pytest nbclient[test] ipyparallel[test]
+          pip freeze
+
+      - name: Run tests
+        run: |
+          pytest --pyargs nbclient
+          pytest --pyargs ipyparallel

ipykernel/comm/comm.py

@@ -66,7 +66,7 @@ def _publish_msg(self, msg_type, data=None, metadata=None, buffers=None, **keys)
         self.kernel.session.send(self.kernel.iopub_socket, msg_type,
             content,
             metadata=json_clean(metadata),
-            parent=self.kernel._parent_header.get('shell', {}),
+            parent=self.kernel._parent_header,
             ident=self.topic,
             buffers=buffers,
         )