Add CI for waydowntown app (#43)

Adapted from @valentynapolienova’s and @jeremyriverain’s articles:

https://medium.com/@m1nori/run-flutter-integration-tests-using-github-actions-workflow-80958948b8e4
https://www.geekco.fr/posts/how-to-add-flutter-integration-test-in-a-ci-with-github-action

.github/workflows/ci-waydowntown-app.yml

@@ -0,0 +1,52 @@
+name: waydowntown_app checks
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    paths:
+      - "waydowntown/waydowntown_app/**"
+      - ".github/workflows/ci-waydowntown-app.yml"
+
+jobs:
+  test-ios:
+    runs-on: macOS-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: futureware-tech/simulator-action@v3
+        with:
+          model: "iPhone 14"
+
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: "stable"
+
+      - run: flutter pub get
+        working-directory: waydowntown/waydowntown_app
+      - run: flutter test
+        working-directory: waydowntown/waydowntown_app
+
+  test-android:
+    runs-on: ubuntu-20.04
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: "stable"
+
+      - run: flutter pub get
+        working-directory: waydowntown/waydowntown_app
+
+      - name: Run integration tests
+        uses: reactivecircus/android-emulator-runner@v2
+        with:
+          working-directory: waydowntown/waydowntown_app
+          api-level: 21
+          arch: x86_64
+          profile: Nexus 6
+          script: flutter test --verbose

README.md

@@ -5,4 +5,5 @@ This is a monorepo to support various adventures.
 - [![Gathering checks](https://github.com/backspace/adventures/actions/workflows/ci-gathering.yml/badge.svg)](https://github.com/backspace/adventures/actions/workflows/ci-gathering.yml) `gathering`: an Ember/PouchDB interface to collect locations
 - [![AdventureRegistrations checks](https://github.com/backspace/adventures/actions/workflows/ci-registrations.yml/badge.svg)](https://github.com/backspace/adventures/actions/workflows/ci-registrations.yml) `registrations`: an Elixir/Phoenix application to advertise and collect registrations
 - [![unmnemonic devices checks](https://github.com/backspace/adventures/actions/workflows/ci-unmnemonic-devices-vrs.yml/badge.svg)](https://github.com/backspace/adventures/actions/workflows/ci-unmnemonic-devices-vrs.yml) `unmnemonic_devices_vrs`: a Rust/Axum server for a Twilio-driven voice response system
+- [![waydowntown app checks](https://github.com/backspace/adventures/actions/workflows/ci-waydowntown-app.yml/badge.svg)](https://github.com/backspace/adventures/actions/workflows/ci-waydowntown-app.yml) `waydowntown_app`: a Flutter app for waydowntown
 - [![waydowntown server checks](https://github.com/backspace/adventures/actions/workflows/ci-waydowntown-server.yml/badge.svg)](https://github.com/backspace/adventures/actions/workflows/ci-waydowntown-server.yml) `waydowntown_server`: a Rails server to back the waydowntown app