chore: Document the multi-tab tests and run them on CI

Author: jcoglan

.github/workflows/ci.yml

@@ -178,6 +178,29 @@ jobs:
         if: steps.retry.outcome == 'failure'
         run: ${{ matrix.cmd }}
 
+  # Run the multitab tests in every supported browser
+
+  multitab:
+    needs: lint
+    strategy:
+      fail-fast: false
+      matrix:
+        client: ['firefox', 'chromium', 'webkit']
+        adapter: ['idb', 'indexeddb']
+    runs-on: ubuntu-latest
+    env:
+      CLIENT: ${{ matrix.client }}
+      ADAPTERS: ${{ matrix.adapter }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - uses: ./.github/actions/install-node-package
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+      - uses: ./.github/actions/build-pouchdb
+      - run: npm run test-multitab
+
   # Run the integration, find and mapreduce tests against all the Node.js
   # PouchDB adapters. This should be run for every adapter on every version of
   # Node.js we support.

TESTING.md

@@ -24,6 +24,7 @@ help fixing them though.
   - [Test options](#test-options)
 - [Other sets of tests](#other-sets-of-tests)
   - [`find` and `mapreduce`](#find-and-mapreduce)
+  - [multi-tab tests](#multi-tab-tests)
   - ["Fuzzy" tests](#fuzzy-tests)
   - [Performance tests](#performance-tests)
   - [Running tests in the browser](#running-tests-in-the-browser)
@@ -239,6 +240,24 @@ like so:
 Note that the default choice for the `SERVER` value (`pouchdb-express-router`)
 does not support `find` or `mapreduce` and does not need to pass these tests.
 
+### Multi-tab tests
+
+We have a few tests to check that interactions with backing stores like
+IndexedDB are synchronized across tabs where multiple PouchDB instances are
+connected to the same database. These have to be scripted via Playwright rather
+than being run inside the normal unit test suite. To run them:
+
+    $ npm run test-multitab
+
+Two environment variables can be used to control how these are run:
+
+- `CLIENT`: may be `firefox`, `chromium` or `webkit` to select the browser where
+  the tests will be run.
+- `ADAPTERS`: may be `idb` or `indexeddb` to set which backend adapter PouchDB
+  will use.
+
+All combinations of these should be tested on CI.
+
 ### "Fuzzy" tests
 
 This test suite checks some more unusual replication scenarios, it can be run