Add job to run tests on pull requests

.github/workflows/test.yml

@@ -0,0 +1,19 @@
+name: Test code
+
+on:
+  push:
+    branches: main
+  pull_request:
+    branches: main
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
+      with:
+        node-version: '20'
+        cache: 'npm'
+    - run: npm ci
+    - run: npm test