There are a variety of automated tests both stand-alone and instrumented for testing on emulators. These are in the app/src/test and app/src/androidTest directories respectively.
Running the stand-alone tests can be done from the command line:
./gradlew :app:testDebugUnitTest
For the instrumented tests, it’s recommended that you run these in Android Studio where you can manage the virtual devices that the tests run on. At the moment the only instrumented tests are those which check the puzzle asset files; these do not have any dependencies on SDK features other than reading the assets, so it should only be necessary to run them on a device with the minimum SDK level (23) and target SDK (37).