[Feature Request] Overriding existing TypeFactory for testing purposes

[rslosarz]

I'd suggest adding a map method for testing purposes, that will allow overriding existing objectKeys. This is quite useful while Unit Testing, where tested object uses some Injected implementation that we'd like to mock.

This is the method I'm thinking of:

void mapWithOverride<T>(ObjectFactoryFn<T> factoryFn,
   {bool isSingleton = false, String key}) {
 final objectKey = _makeKey(T, key);
 if (_factories.containsKey(objectKey)) {
   _factories.remove(objectKey); //override instead of throwing exception
 }
 _factories[objectKey] =
 new TypeFactory<T>((i, p) => factoryFn(i), isSingleton);
}

This is the case I'm talking about: This is tested object:

class SomeRepository implements RepoInterface {
  final SomeSourceInterface source = Injector.getInjector().get<SomeSourceInterface>();
  @override
  List<Results> getResults() {
    List<Results> list = source.getObjects();
    (...) //some data processing, repo pattern etc.
  }
}

This is class handling DI initialisation:

//Class used to 
class InjectionInit {
  static void init() {
    final injector = Injector.getInjector();
    injector.map<SomeSourceInterface>((i) => new ProdImplementation());
  }
}

Normally used like this:

void main() {
  InjectionInit.init();
  runApp(App());
}

And this is Unit Test class where I'd like to mock SomeSourceInterface:

import 'package:flutter_simple_dependency_injection/injector.dart';
import 'package:test_api/test_api.dart';
import 'package:mockito/mockito.dart';

class MockImplementation extends Mock implements SomeSourceInterface {}

void main() {
  group('SomeRepository tests', () {
    SomeRepository repo;
    MockImplementation source;

    setUpAll(() {
      InjectionInit.init();
      source = new MockImplementation();
      final injector = Injector.getInjector();
      injector.mapWithOverride<SomeSourceInterface>((i) => source);
    });

    setUp(() {
      repo = new SomeRepository();
    });

    tearDown(() {
      repo = null;
    });

    test('test', (){
      when(source.getObjects()).thenReturn(...);
      (...)
    });
  });
}

[jonsamwell]

@rslosarz I would just like to understand how you are using the DI.

I would strongly advise that no service or component or anything is dependent on the injector. I would always ensure a service's dependencies are injected into that service rather than the service knowing about the injector and getting them itself. This will help to stop the scenario you have just encountered.

As a general rule if you are using the injector outside of initializing it you are doing something wrong.

Therefore, I would ensure the above service looks something like this.

class SomeRepository implements RepoInterface {
  final SomeSourceInterface _source;

  SomeRepository(this._source);

  @override
  List<Results> getResults() {
    List<Results> list = _source.getObjects();
    (...) //some data processing, repo pattern etc.
  }
}

class InjectionInit {
  // pass in an injector instance so you are not coupled to static methods
  static void init(Injector injector) {
    injector.map<SomeSourceInterface>((i) => new ProdImplementation());
    injector.map<SomeRepository>((i) => new SomeRepository(i.get<SomeSourceInterface>()));
  }
}

Then your test would look like this:

import 'package:flutter_simple_dependency_injection/injector.dart';
import 'package:test_api/test_api.dart';
import 'package:mockito/mockito.dart';

class MockImplementation extends Mock implements SomeSourceInterface {}

void main() {
  group('SomeRepository tests', () {
    SomeRepository repo;
    MockImplementation source;

    setUp(() {
      source = new MockImplementation();
      repo = new SomeRepository(source);
    });

    tearDown(() {
      repo = null;
    });

    test('test', (){
      when(source.getObjects()).thenReturn(...);
      (...)
    });
  });
}

I hope this help. Let me know your thoughts.

[jonsamwell]

@rslosarz did this approach help?