Flutter Mockito 测试模拟失败

Question

I am trying to mock a repository in my Flutter Widget test case but each time I run the test I encounter an error as shown below.

package:quiz_test/level/repository/LevelRepository.dart 6:23   MockLevelRepository.fetchLevels
test/unit/level/view_model/LevelSelectionViewModel.dart 46:30  main.<fn>
test/unit/level/view_model/LevelSelectionViewModel.dart 32:38  main.<fn>

type 'Null' is not a subtype of type 'Future<List<Level>>'

This is my test case (I will improve the test name later).

  test('Waiting for an interaction', () async {
    final mockLevelRepository = MockLevelRepository();

    List<Level> levelsList = <Level>[];

    Level level = Level(id: 1, name: "Level 1");
    levelsList.add(level);

    level = Level(id: 2, name: "Level 2");
    levelsList.add(level);

    level = Level(id: 3, name: "Level 3");
    levelsList.add(level);

    when(mockLevelRepository.fetchLevels())
        .thenAnswer((_) async => Future.value(levelsList));

    LevelSelectionViewModel levelSelectionViewModel =
        new LevelSelectionViewModel();
    levelSelectionViewModel.setRepository(mockLevelRepository);

    levelSelectionViewModel.fetchLevels();
  });

I appreciate at this point I'm not 'testing' for anything, I just want to get it to pass as is. Having said that I'm not sure either how to handle this since it returns a future.

As can be seen I've mocked the repository. If I put a breakpoint on the line levelSelectionViewModel.fetchLevels(); it is never hit.

The entire file is:

LevelSelectionViewModelTest

import 'package:flutter/material.dart';
import 'package:mockito/mockito.dart';
import 'package:quiz_test/level/repository/LevelRepository.dart';
import 'package:quiz_test/level/view_model/LevelSelectionViewModel.dart';
import 'package:quiz_test/models/Level.dart';
import 'package:test/test.dart';

class MockLevelRepository extends Mock implements LevelRepository {}

void main() {
  test('Test isLevelLocked returns correct response', () {
    bool response = LevelSelectionViewModel().isLevelLocked(1);
    expect(response, false);

    response = LevelSelectionViewModel().isLevelLocked(2);
    expect(response, false);

    response = LevelSelectionViewModel().isLevelLocked(3);
    expect(response, false);

    response = LevelSelectionViewModel().isLevelLocked(0);
    expect(response, true);

    response = LevelSelectionViewModel().isLevelLocked(4);
    expect(response, true);
  });

  test('Waiting for an interaction', () async {
    final mockLevelRepository = MockLevelRepository();

    List<Level> levelsList = <Level>[];

    Level level = Level(id: 1, name: "Level 1");
    levelsList.add(level);

    level = Level(id: 2, name: "Level 2");
    levelsList.add(level);

    level = Level(id: 3, name: "Level 3");
    levelsList.add(level);

    when(mockLevelRepository.fetchLevels())
        .thenAnswer((_) async => Future.value(levelsList));

    LevelSelectionViewModel levelSelectionViewModel =
        new LevelSelectionViewModel();
    levelSelectionViewModel.setRepository(mockLevelRepository);

    levelSelectionViewModel.fetchLevels();
  });
}

LevelRepository

import 'dart:convert';
import 'package:flutter/services.dart';
import 'package:quiz_test/models/Level.dart';

class LevelRepository {
  Future<List<Level>> fetchLevels() async {
    final jsondata =
        await rootBundle.loadString('assets/data/levels/Levels.json');

    final body = jsonDecode(jsondata);
    final Iterable json = body["Items"];
    return json.map((level) => Level.fromJson(level)).toList();
  }
}

LevelSelectionViewModel

import 'package:flutter/material.dart';
import 'package:quiz_test/level/repository/LevelRepository.dart';
import '../../models/Levels.dart';

class LevelSelectionViewModel extends ChangeNotifier {
  late LevelRepository levelRepository;

  // ToDo - Need to identify how to watch 'levels' instead.
  bool changed = false;
  List<Levels> levels = <Levels>[];

  void setRepository(LevelRepository levelRepository) {
    this.levelRepository = levelRepository;
  }

  Future<void> fetchLevels() async {
    final results = await levelRepository.fetchLevels();
    this.levels = results.map((item) => Levels(level: item)).toList();
    changed = true;
    notifyListeners();
  }

  // ToDo - These are hard coded for now... will change later.
  bool isLevelLocked(int levelNumber) {
    if (levelNumber >= 1 && levelNumber <= 3) return false;
    return true;
  }
}

Note: I have tried adding @GenerateMocks([LevelSelectionViewModel, LevelRepository])

just before main() in my test file but that did not resolve my issue.

So I have two issues here:

a) How do I fix the error? I can't understand what the problem is. I read that it could be about nullability but I'm not sure 'why' that is an issue here. The other potential issue was the type was wrong but I don't see that that's the problem here either.

b) Since the fetchLevels call returns a Future, how should I test that this method is doing what it should. Ultimately I think I'd need to perhaps 'watch' to be notified.

It's worth noting that I am using get_in and get_in_mixer. I am testing using Mockito.

Any help is very much appreciated.

Answer 1

So, I can now answer the first part of this. In short I should have paid more attention to the Mockito documentation as the answers were all there.

a) I added the @GenerateMocks annotation

@GenerateMocks([LevelRepository])
void main() {
  test('Test isLevelLocked returns correct response', () {
    bool response = LevelSelectionViewModel().isLevelLocked(1);

b) I added build_runner: ^2.1.5 to pubspec.yml

c) I ran flutter pub get

d) I ran flutter packages pub run build_runner build

e) I added the new import import 'LevelSelectionViewModel.mocks.dart'; to my test file.

The test then ran to completion. All that's left now is for me to understand how to test this future.