How to pass an environment variable to a flutter driver test

Question

I want to pass an environment variable to a flutter drive test.

Being able to read the value in the launched application or the test code would both be fi

Answer 1

I encountered the same need to pass an environment variable for test application on a device in a Flutter driver test. The challenge was that test applications cannot read environment variables directly from flutter drive command.

Here is how I solved the problem. The test name for is "field_value_behaviors.dart". Environment variable name is FIRESTORE_IMPLEMENTATION.

Flutter Drive Command

Specify environment variable when running flutter drive command:

$ FIRESTORE_IMPLEMENTATION=cloud_firestore flutter drive --target=test_driver/field_value_behaviors.dart

Driver Program

Driver program ("field_value_behaviors_test.dart") runs as part of flutter drive program. It can read environment variables:

  String firestoreImplementation =
      Platform.environment['FIRESTORE_IMPLEMENTATION'];

Further, the driver program sends the value to test application running on a device through driver.requestData.

  final FlutterDriver driver = await FlutterDriver.connect();
  // Sends the choice to test application running on a device
  await driver.requestData(firestoreImplementation);
  await driver.requestData('waiting_test_completion',
      timeout: const Duration(minutes: 1));
  ...

Test Application

Test application ("field_value_behaviors.dart") has group() and test() function calls and runs on a device (simulator). Therefore it cannot read the environment variable directly from flutter drive command. Luckily, the test application can receive String messages from the driver program through enableFlutterDriverExtension():

void main() async {
  final Completer firestoreImplementationQuery = Completer();
  final Completer completer = Completer();

  enableFlutterDriverExtension(handler: (message) {
    if (validImplementationNames.contains(message)) {
      // When value is 'cloud_firestore' or 'cloud_firestore_mocks'
      firestoreImplementationQuery.complete(message);
      return Future.value(null);
    } else if (message == 'waiting_test_completion') {
      // Have Driver program wait for this future completion at tearDownAll.
      return completer.future;
    } else {
      fail('Unexpected message from Driver: $message');
    }
  });
  tearDownAll(() {
    completer.complete(null);
  });

The test application changes the behavior based on the resolved value of firestoreImplementationQuery.future:

  firestoreFutures = {
    // cloud_firestore_mocks
    'cloud_firestore_mocks': firestoreImplementationQuery.future.then((value) =>
        value == cloudFirestoreMocksImplementationName
            ? MockFirestoreInstance()
            : null),

Conclusion: read environment variable by Platform.environment in your driver program. Pass it to your test application by driver.requestData argument.

The implementation is in this PR: https://github.com/atn832/cloud_firestore_mocks/pull/54