add GitHub Action to run unit tests on every PR/push

.github/workflows/run-tests.yml

@@ -0,0 +1,27 @@
+name: Run Unit Tests
+
+on:
+  push:
+    branches: [ $default-branch ]
+  pull_request:
+    branches: [ $default-branch ]
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [12.x, 14.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 ci
+    - run: npm test