Play with docker build

.github/workflows/docker.yml

@@ -0,0 +1,23 @@
+name: Docker
+
+on:
+  - push
+
+jobs:
+  docker:
+    name: 'Docker: Build'
+    runs-on: ubuntu-20.04
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v2
+        with:
+          push: false
+          context: .
+          target: test
+          tags: "gmmcal:test"
+      - name: Test
+        run: |
+          docker run --rm gmmcal:test

.gitignore

@@ -9,6 +9,7 @@ capybara-*.html
 /public/assets
 /public/uploads
 /coverage/
+!/coverage/.keep
 /spec/tmp
 /spec/backend/examples.txt
 /spec/end-to-end/screenshots