Unit-testing function with isolates and compute in flutter

Question

I'm trying to test a widget that receives and displays some data. This widget uses a controller. In the constructor I start receiving data, after which I execute the parser in a separate isolate. During the tests, the function passed to the compute is not executed until the end, and the widget state does not change. In fact, the structure of the widget looks a little more complicated, but I wrote smaller widget that saves my problem:

import 'dart:convert';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:rxdart/rxdart.dart';

class TestObj {
  int id;
  String name;
  String number;

  TestObj(this.id, this.name, this.number);

  static List<TestObj> jsonListParser(String data) {
    List mapObjs = json.decode(data) as List;
    if (mapObjs.isEmpty) return [];

    List<TestObj> testObjs = [];

    for (final Map mapObj in mapObjs as List<Map>)
      testObjs.add(
        TestObj(
          mapObj['id'] as int,
          mapObj['name'] as String,
          mapObj['number'] as String,
        ),
      );

    return testObjs;
  }
}

class TestController {
  final BehaviorSubject<List<TestObj>> testSubj;
  final String responseBody =
      '[{"id":2,"number":"1","name":"Объект 1"},{"id":1,"number":"2","name":"Объект 2"}]';

  TestController(this.testSubj) {
    getData(responseBody, testSubj);
  }

  Future<void> getData(
      String responseBody, BehaviorSubject<List<TestObj>> testSubj) async {
    List<TestObj> data = await compute(TestObj.jsonListParser, responseBody);
    testSubj.sink.add(data);
  }
}

class TestWidget extends StatelessWidget {
  final BehaviorSubject<List<TestObj>> testSubj;
  final TestController controller;

  const TestWidget(this.testSubj, this.controller);

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<List<TestObj>>(
      stream: testSubj.stream,
      builder: (context, snapshot) => snapshot.data == null
          ? const CircularProgressIndicator()
          : ListView.builder(
              itemBuilder: (context, index) => Text(snapshot.data[index].name),
            ),
    );
  }
}

void main() {
  testWidgets('example test', (tester) async {
    final BehaviorSubject<List<TestObj>> testSubj =
        BehaviorSubject.seeded(null);
    final TestController testController = TestController(testSubj);

    await tester.pumpWidget(
      TestWidget(testSubj, testController),
    );

    expect(find.byType(CircularProgressIndicator), findsNothing);
  });
}

I have tried using tester.pump, tester.pumpAndSettle (crashed by timeout) and tester.runAsync, but so far without success. What are the solutions of this problem?

Answer 1

As indicated in runAsync docs, it is not supported to have isolates/compute in tests that are proceeded by pump().

To make a self-contained solution, check if you run in test environment or not in your code and skip isolates when you run in a test:

import 'dart:io';

if (!kIsWeb && Platform.environment.containsKey('FLUTTER_TEST')) {
  calc()
} else {
  calcInIsolate()
}