Browser testing framework

.github/workflows/browser-test.yml

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+name: Browser Test
+
+on:
+  pull_request:
+
+jobs:
+  browser-test:
+    runs-on: 'ubuntu-22.04'
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      - run: python -m pip install --upgrade pip
+      - run: pip install -r requirements/test.txt
+      - run: pip install -r requirements/docs.txt
+      - run: pip install jupyterlab pytest-playwright
+      - run: pip install -e .
+      - run: playwright install firefox --with-deps  # Install a browser
+      - run: nohup jupyter lab --NotebookApp.token='' --NotebookApp.password='' --no-browser &  # Start a JupyterLab server
+      - run: pytest tests/applications/playwright_testing.py --browser firefox

tests/applications/playwright_testing.py

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+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2024 Scipp contributors (https://github.com/scipp)
+# This file does not have the suffix "_test" in its name.
+# It is because these tests are excluded from the other unit tests
+# and are used for testing the Playwright testing framework.
+# One of blocker issues is that the playwright fixture holds on an event loop
+# but some of other tests require a clean event loop.
+import pytest
+from playwright.sync_api import Page, expect
+
+_EXPECTED_JUPYTER_LAB_ADDRESS = "http://localhost:8888/lab"
+
+
+@pytest.fixture()
+def jupyter_lab_running(page: Page) -> bool:
+    """Skip tests if jupyter lab is not running in the background."""
+    try:
+        # Try opening the Jupyter Lab page.
+        page.goto(_EXPECTED_JUPYTER_LAB_ADDRESS)
+    except Exception as e:
+        page.close()
+        # Playwright does not have different error objects for different errors.
+        # And error messages differ from browser to browser/OS.
+        # So we skip all tests on any error going to the Jupyter Lab page.
+        pytest.skip(
+            f"Jupyter Lab is not running at {_EXPECTED_JUPYTER_LAB_ADDRESS}."
+            "Check if jupyter lab is running without TOKEN or PASSWORD"
+            "and the address is correct.\n"
+            f"Raised error: {e}"
+        )
+    return True
+
+
+def test_jupyter_lab_server_available(jupyter_lab_running: bool, page: Page) -> None:
+    # Expect a title "to contain" a substring.
+    assert jupyter_lab_running
+    page.goto(_EXPECTED_JUPYTER_LAB_ADDRESS)
+    expect(page).to_have_title("JupyterLab")