Create build workflow, add tests

.github/workflows/build.yml

@@ -0,0 +1,33 @@
+# This workflow will do a clean installation of node dependencies, cache/restore them, build the
+# source code and run tests across different versions of node For more information see:
+# https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-nodejs
+
+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@v4
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v4
+      with:
+        node-version: ${{ matrix.node-version }}
+        cache: 'npm'
+    - run: npm ci
+    - run: npm run build --if-present
+
+    # TODO use a headless browser to execute tests.
+    #- run: npm run test

DEVELOP.md

@@ -27,7 +27,15 @@ $ npm run build
 To view a demo HTML page that displays the available icons:
 
 ```shell
-$ npm run serve
+$ npm run start
 ```
 
-Now you can visit the host web page at `localhost:8080`.
+Now you can visit the demo page at `localhost:8080` (it should open in your browser automatically).
+
+To run the unit tests:
+
+```shell
+$ npm run test
+```
+
+Now you can visit the test page at `localhost:8080` (it should open in your browser automatically).