Enable continuous testing with GitHub Actions.

.github/workflows/run_tests.yml

@@ -0,0 +1,26 @@
+name: Node.js CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+
+    runs-on: [ubuntu-latest]
+
+    strategy:
+      matrix:
+        node-version: [18.x, 20.x]
+
+    steps:
+      - uses: actions/checkout@v3
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v3
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm install
+      - run: npm run build --if-present
+      - run: npm test