How to use --dart-define-from-file in Flutter test

This is NOT the same question as How to use --dart-define in Flutter test

Using the Flutter 3.7 release, I am loading config/env variables to my Flutter app at runtime using the command flutter run --dart-define-from-file=config.json. For testing, how would I make sure a test config file is loading at runtime?

You could create a new separate configuration file ("test_config.json" for example) that contains the test environment variables to be loaded during testing.

flutter test --dart-define-from-file=test_config.json

Make sure to load the proper configuration file in your app. Assuming that you are using flutter_config:

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await FlutterConfig.loadEnvVariables();

  runApp(MyApp());
}

It ensures that the test configuration file is loaded at runtime during testing, allowing testing with the desired environment variables or configurations.

Additionally, you could use the loadValueForTesting in the flutter_config package to load mock variables:

void main() {
  FlutterConfig.loadValueForTesting({'BASE_URL': 'https://www.mockurl.com'});
  
  test('mock http client test', () {
    final client = HttpClient(
      baseUrl: FlutterConfig.get('BASE_URL')
    );
  });
}