Add workflow to test JupyterLab

.github/workflows/downstream.yml

@@ -0,0 +1,31 @@
+name: Test JupyterLab
+
+on:
+  push:
+    branches: "*"
+  pull_request:
+    branches: "*"
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+
+      - name: Install dependencies
+        run: |
+          pip install --upgrade pip
+          pip install "."
+          pip install --pre --upgrade jupyterlab[test]
+          pip freeze
+      - name: Run tests
+        run: |
+          python -m jupyterlab.browser_check --no-browser-test