Add tests

.github/workflows/testing.yml

@@ -0,0 +1,45 @@
+name: Back-end Tests
+on:
+  schedule:
+    - cron: "0 16 * * *"  # Daily at noon EST
+  pull_request:
+
+concurrency:  # Cancel previous workflows on the same pull request
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  CACHE_NUMBER: 2  # increase to reset cache manually
+
+jobs:
+  testing:
+    name: Back-end tests on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    defaults:
+      run:
+        shell: bash -l {0}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+
+    steps:
+      - uses: actions/checkout@v3
+      - run: git fetch --prune --unshallow --tags
+
+      - name: Set cache date
+        id: get-date
+        run: echo "today=$(/bin/date -u '+%Y%m%d')" >> $GITHUB_OUTPUT
+        shell: bash
+
+      - name: Use Node.js 18
+        uses: actions/setup-node@v3
+        with:
+          node-version: 18
+
+      - name: Install Commoners
+        run: npm ci
+
+      - name: Run tests
+        run: npm run test:coverage