Add GitHub action to test build. (#27)

.github/workflows/build-test.yml

@@ -0,0 +1,27 @@
+name: NPM build + test
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node: [ '18' ]
+
+    name: Node ${{ matrix.node }} build
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
+        with:
+          path: ~/.npm
+          key: ${{ runner.os }}-${{ matrix.node }}-npm-${{ hashFiles('**/package-lock.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-npm-
+      - name: Setup node
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node }}
+
+      - run: npm ci
+      - run: npm run build