Add unit test GH action

.github/workflows/main.yml

@@ -0,0 +1,33 @@
+name: Unit tests
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+  # Allows to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      # Checks-out the repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - name: Use Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: '12.x'
+
+      - name: Install elm
+        run: |
+          curl -L -o elm.gz https://github.com/elm/compiler/releases/download/0.19.1/binary-for-linux-64-bit.gz
+          gunzip elm.gz
+          chmod +x elm
+          sudo mv elm /usr/local/bin/
+          
+      - name: Run elm-test
+        run: npx elm-test