add Node.js test action to GitHub workflows (#294)

* Create nodejs.yml

* `npm i` rather than `npm ci`

since this project uses yarn.lock rather than package-lock.json

* use multiple lines for node-version

* use matrix to run on macOS & Windows

  (skip Ubuntu for now, at least)

* add Node.js 8

* add comment with matrix ref links

Author: Chris Brody

.github/workflows/nodejs.yml

@@ -0,0 +1,40 @@
+# This workflow will do a clean install of node dependencies, build the source code and run tests across different versions of node
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-nodejs-with-github-actions
+
+name: Node.js CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      # ref:
+      # - https://help.github.com/en/actions/configuring-and-managing-workflows/configuring-a-workflow#configuring-a-build-matrix
+      # - https://help.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstrategymatrix
+      matrix:
+        os:
+        - macos-latest
+        - windows-latest
+        node-version:
+        - 8.x
+        - 10.x
+        - 12.x
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm i
+    - run: npm run build --if-present
+    - run: npm test
+      env:
+        CI: true