[integration_test] allow custom binding initialization when running integration_test tests

[bartekpacia]

This is a revival of, and copy-paste from, #92254. We need the feature mentioned in there in our Patrol testing framework.

Use case

I'd like to be in control of the test binding I choose for integration tests. In my case, I have a custom binding to set the TestBindingEventSource of all touch events as test, not device.

That's how my custom binding looks like.

The cookbook contains documentation about adding the ensureInitialized call, but (at least on the latest beta version) flutter run and flutter test generate an intermediate file that calls:

IntegrationTestWidgetsFlutterBinding.ensureInitialized();

That intermediate file is called listener.dart autogenerated in a path like /var/folders/z8/vl6s_16515s6h_j8z7bs1tmm0000gn/T/flutter_tools.LfIUH0/flutter_test_listener.SK8Sr1/listener.dart. To find its location, run flutter test integration_test -v (without -v the path to the autogenerated file is not shown).

Here's its code:

listener.dart

Here's the method which generates this file.

// @dart=2.17
import 'dart:async';
import 'dart:convert';  // flutter_ignore: dart_convert_import
import 'dart:io';  // flutter_ignore: dart_io_import
import 'dart:isolate';
import 'package:flutter_test/flutter_test.dart';
import 'package:integration_test/integration_test.dart';
import 'dart:developer' as developer;
import 'package:test_api/src/remote_listener.dart';
import 'package:stream_channel/stream_channel.dart';
import 'package:stack_trace/stack_trace.dart';

import 'file:///Users/bartek/dev/leancode/patrol/packages/patrol/example/integration_test/example_test.dart' as test;

/// Returns a serialized test suite.
StreamChannel<dynamic> serializeSuite(Function getMain()) {
  return RemoteListener.start(getMain);
}

Future<void> _testMain() async {
  IntegrationTestWidgetsFlutterBinding.ensureInitialized();
  await Future(test.main);
}

/// Capture any top-level errors (mostly lazy syntax errors, since other are
/// caught below) and report them to the parent isolate.
void catchIsolateErrors() {
  final ReceivePort errorPort = ReceivePort();
  // Treat errors non-fatal because otherwise they'll be double-printed.
  Isolate.current.setErrorsFatal(false);
  Isolate.current.addErrorListener(errorPort.sendPort);
  errorPort.listen((dynamic message) {
    // Masquerade as an IsolateSpawnException because that's what this would
    // be if the error had been detected statically.
    final IsolateSpawnException error = IsolateSpawnException(
        message[0] as String);
    final Trace stackTrace = message[1] == null ?
        Trace(const <Frame>[]) : Trace.parse(message[1] as String);
    Zone.current.handleUncaughtError(error, stackTrace);
  });
}

void main() {
  String serverPort = Platform.environment['SERVER_PORT'] ?? '';
  String server = Uri.decodeComponent('ws%3A%2F%2F127.0.0.1:$serverPort');
  StreamChannel<dynamic> testChannel = serializeSuite(() {
    catchIsolateErrors();
    goldenFileComparator = LocalFileComparator(Uri.parse('file:///Users/bartek/dev/leancode/patrol/packages/patrol/example/integration_test/example_test.dart'));
    autoUpdateGoldenFiles = false;
    return _testMain;
  });
  final callback = (method, params) async {
    testChannel.sink.add(json.decode(params['data'] as String));

    // Result is ignored but null is not accepted here.
    return developer.ServiceExtensionResponse.result('{}');
  };

  developer.registerExtension('ext.flutter.integrationTest', callback);

  testChannel.stream.listen((x) {
    developer.postEvent(
      'Flutter.IntegrationTest',
      {'data': json.encode(x)},
    );
  });
} 

Proposal

Remove ensureInitialized from the generated file so users can choose what binding (and what configuration) they want the test to use (or at least allow to initialize only subclasses of IntegrationTestWidgetsFlutterBinding).

Also I think that generating this file is not communicated clearly enough (or at all) by the integration testing docs, which are focused only on very simple cases.

[goderbauer]

cc @pdblasi-google

[bartekpacia]

Hi @pdblasi-google, I see you wrote this comment, but since that issue is locked no one can respond there, so I'm gonna do it here.

I contacted @Norbert515 personally some time ago asking him the same question, and that's what he responded:

Hi Bartek, it’s been a while but I just looked through my old code and it seems like I was generating a proxy main file that calls these bindings before calling the user's main

This sounds like a clever but ugly hack. As a developer of a new testing framework for Flutter, I'd love to get the ability to just use my own binding class extending IntegrationTestWidgetsFlutterBinding.

[bartekpacia]

This issue essentially comes down to removing this from the flutter_tools generateTestBootstrap() function.

final StringBuffer buffer = StringBuffer();

// ...

// TOOD: Remove this if and its contents
if (integrationTest) {
    buffer.write('''
  IntegrationTestWidgetsFlutterBinding.ensureInitialized();
''');

This will require users to manually initialize their bindings (which is a single line), but will enable using custom bindings.