tests/plugins: checkPlugins backend tests config

Tnx to @webzwo0i 👍

bin/plugins/lib/backend-tests.yml

@@ -0,0 +1,51 @@
+# You need to change lines 38 and 46 in case the plugin's name on npmjs.com is different
+# from the repository name
+
+name: "Backend tests"
+
+# any branch is useful for testing before a PR is submitted
+on: [push, pull_request]
+
+jobs:
+  withplugins:
+    # run on pushes to any branch
+    # run on PRs from external forks
+    if: |
+         (github.event_name != 'pull_request')
+         || (github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id)
+    name: with Plugins
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Install libreoffice
+      run: |
+        sudo add-apt-repository -y ppa:libreoffice/ppa
+        sudo apt update
+        sudo apt install -y --no-install-recommends libreoffice libreoffice-pdfimport
+
+    # clone etherpad-lite
+    - name: Install etherpad core
+      uses: actions/checkout@v2
+      with:
+        repository: ether/etherpad-lite
+
+    - name: Install all dependencies and symlink for ep_etherpad-lite
+      run: bin/installDeps.sh
+
+    # clone this repository into node_modules/ep_plugin-name
+    - name: Checkout plugin repository
+      uses: actions/checkout@v2
+      with:
+        path: ./node_modules/${{github.event.repository.name}}
+
+    - name: Install plugin dependencies
+      run: |
+        cd node_modules/${{github.event.repository.name}}
+        npm ci
+
+    # configures some settings and runs npm run test
+    - name: Run the backend tests
+      run: tests/frontend/travis/runnerBackend.sh
+
+##ETHERPAD_NPM_V=1
+## NPM configuration automatically created using bin/plugins/updateAllPluginsScript.sh