How to mock the library in widget tests? about flutter-translate

[xzhorikx]

I've just spent two hours configuring all the required things, but I've made the following approach:

1. Create a simple service class that would have a transaltion method (i.e. String safeTranslate(String key)).
2. Use DI/Service Locator to get said service in class
3. Call safeTranslate(key) every time I need a translation

Example:

1. Creating TranslateService

I use get_it and injectable as a service locator in my app.

import 'package:flutter_translate/flutter_translate.dart' as globalTranslate;
import 'package:injectable/injectable.dart';

/// Implementation that is registered in GetIt service locator
@RegisterAs(TranslateService)
@injectable
class TranslateServiceImpl implements TranslateService {
  @override
  String safeTranslate(String key) {
    try{
      return globalTranslate.translate(key);
    } catch(Exception){
      return "translation.error";
    }
  }
}

/// Abstract translate service
abstract class TranslateService {
  String safeTranslate(String key);
}

2. Use DI/Service locator in tested class

At this point, you need to configure GetIt - go through their tutorials on pages linked above and all should be safe and sound. Two notes that are not mentioned in tutorials:

• Make sure to add test/** source folder in build.yaml
• run flutter packages pub run build_runner watch test once configured to generate test dependencies

import 'package:get_it/get_it.dart';
...

/// Class that will be tested
class TestedClass {
  /// Instance of TranslateService that is provided by GetIt (service locator)
  final TranslateService _translateService = GetIt.instance.get();
  
  // Some method that uses translation
  String doSomeStuff() {
    return _translateService.safeTranslate("translation_key")
  }
}

3. Testing a class that requires translation

• Create your_class_test.dart file under test folder

/// Important: GetIt needs to be initialized in a top level function
@injectableInit
void configureInjection(String environment) =>
    $initGetIt(GetIt.instance, environment: environment);

void main() {

  configureInjection("Some env value");

  FlutterTest.test("Date formatter: today date", (){
    /// Translation service should be located once class is created
    final TestedClass testedClass  = TestedClass();
    String safeTranslation = testedClass.doSomeStuff(); <--- no exception here
    ...
  });

[IlyaMax]

@VytorCalixto you can call Localization.load(<String,dynamic>{}); before tests and error won't be thrown