How to pass an environment variable to a flutter driver test

The .env package serves me well:

include:

import 'package:dotenv/dotenv.dart' show load, env;

load:

load();

use:

test('can log in', () async {
      await driver.tap(emailFieldFinder);
      await driver.enterText(env['USERNAME']);
      await driver.tap(passwordFieldFinder);
      await driver.enterText(env['PASSWORD']);
      await driver.tap(loginButtonFinder);

      await Future<Null>.delayed(Duration(seconds: 2));

      expect(await driver.getText(mainMessageFinder), "Welcome");
});

I tried using Dart's Platform.environment to read in env variables before running driver tests and it seems to work fine. Below is a simple example that sets the output directory for the test summaries using the FLUTTER_DRIVER_RESULTS env variable.

import 'dart:async';
import 'dart:io' show Platform;

import 'package:flutter_driver/flutter_driver.dart';
import 'package:test/test.dart';

void main() {
  // Load environmental variables
  String resultsDirectory =
    Platform.environment['FLUTTER_DRIVER_RESULTS'] ?? '/tmp';
  print('Results directory is $resultsDirectory');

  group('increment button test', () {
    FlutterDriver driver;

    setUpAll(() async {
      // Connect to the app
      driver = await FlutterDriver.connect();
    });

    tearDownAll(() async {
      if (driver != null) {
        // Disconnect from the app
        driver.close();
      }
    });

    test('measure', () async {
      // Record the performance timeline of things that happen
      Timeline timeline = await driver.traceAction(() async {
        // Find the scrollable user list
        SerializableFinder incrementButton = find.byValueKey(
            'increment_button');

        // Click the button 10 times
        for (int i = 0; i < 10; i++) {
          await driver.tap(incrementButton);

          // Emulate time for a user's finger between taps
          await new Future<Null>.delayed(new Duration(milliseconds: 250));
        }

      });
        TimelineSummary summary = new TimelineSummary.summarize(timeline);
        summary.writeSummaryToFile('increment_perf',
            destinationDirectory: resultsDirectory, pretty: true);
        summary.writeTimelineToFile('increment_perf',
            destinationDirectory: resultsDirectory, pretty: true);
    });
  });
}

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<String> firestoreImplementationQuery = Completer<String>();
  final Completer<String> completer = Completer<String>();

  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