Unit Testing

Note

If you’re experiencing issues running unit tests with Jest and Transloco due to the ESM version of the flat library—commonly encountering an error like:

Error while trying to load ‘en’: TypeError: (0 , import_flat.flatten) is not a function

You can resolve this issue by upgrading to Transloco version 7.5.1 or higher, as the flat dependency was removed starting from that version.

When running tests, it's important to have the languages available immediately and synchronously. Transloco provides the TranslocoTestingModule, which allows you to specify the languages and configuration needed for your specs.

To follow the DRY (Don't Repeat Yourself) principle, it's a good idea to create a module factory function that can be reused in each spec. Here's an example:

transloco-testing.module.ts

import { TranslocoTestingModule, TranslocoTestingOptions } from '@jsverse/transloco';
import en from '../assets/i18n/en.json';
import es from '../assets/i18n/es.json';

export function getTranslocoModule(options: TranslocoTestingOptions = {}) {
  return TranslocoTestingModule.forRoot({
    langs: { en, es },
    translocoConfig: {
      availableLangs: ['en', 'es'],
      defaultLang: 'en',
    },
    preloadLangs: true,
    ...options,
  });
}

Using the module in your spec files

app.component.spec.ts

describe('AppComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [getTranslocoModule()],
      declarations: [AppComponent],
    }).compileComponents();
  }));

  it('should work', () => {
    const fixture = TestBed.createComponent(AppComponent);
    fixture.detectChanges();
    expect(
      fixture.debugElement.query(By.css('h1')).nativeElement.innerText
    ).toBe('hello');
  });
});

You can find a full example here.

Testing scopes

If you need to test scopes, you should add them as languages. For example:

transloco-testing.module.ts

export function getTranslocoModule(options: TranslocoTestingOptions = {}) {
  return TranslocoTestingModule.forRoot({
    langs: {
      en,
      es,
      'admin-page/en': admin,
      'admin-page/es': adminSpanish,
    },
    translocoConfig: {
      availableLangs: ['en', 'es'],
      defaultLang: 'en',
    },
    preloadLangs: true,
    ...options,
  });
}

You can find an example here.

TypeScript Configuration

To import JSON files in your TypeScript project, you need to update your tsconfig.json with the following properties:

{
  "resolveJsonModule": true,
  "esModuleInterop": true
}