Advice on testing Angular $localize (Angular 9)

Issue

Example repo

The repo can be found here.

Please note that this isn't a complete example, it is merely there to show issues around testing $localize.

There are 2 branches: 1. master 1. enable-localize-unit-tests - this changes the test.ts and polyfills.ts to prevent the @angular/localize/init from being imported, the $localize global function is also spied

Overview

I have upgraded a project from Angular 8 to 9 (following the Angular update guide), replacing any usage the I18n service (from the ngx-translation/i18n-polyfill) with Angular's new $localize function (documentation on this is pretty limited, here is the best I could find). I can run localised builds and serve the application in a particular locale again. However, I've hit a bit of a roadblock when it comes to unit testing.

Previously, when using the i18n-polyfill, the I18n service could be injected into components, etc. as follows (see I18nPolyfillComponent):

@Component({
  selector: "app-i18-polyfill",
  template: `<h4>{{ title }}</h4>
})
export class I18nPolyfillComponent {
  readonly title: string = this.i18n({
    id: "title",
    value: "Hello World!"
  });

  constructor(private i18n: I18n) {}
}

This could easily tested by injecting a spy into the component:

describe("I18nPolyfillComponent", () => {
 let component: I18nPolyfillComponent;
 let fixture: ComponentFixture<I18nPolyfillComponent>;

  let mockI18n: Spy;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ I18nPolyfillComponent ],
      providers: [
        {
          provide: I18n,
          useValue: jasmine.createSpy("I18n"),
        },
      ],
    })
      .compileComponents().then(() => {
        mockI18n = TestBed.inject(I18n) as Spy;
    });
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(I18nPolyfillComponent);
    component = fixture.componentInstance;

    mockI18n.and.callFake((def: I18nDef) => def.value);
  });

  it("should call i18n once", () => {
    expect(mockI18n).toHaveBeenCalledTimes(1);
  });
});

However, I am unsure if similar unit tests could be written to test the usage of $localize as it is a global function rather than an injectable service.

For completeness the component would look like this using $localize (see I18nLocalizeComponent):

@Component({
  selector: "app-i18n-localize",
  template: `<h4>{{ title }}</h4>
})
export class I18nLocalizeComponent {
  readonly title: string = $localize `:@@title:Hello World!`;
}

Testing rationale

I would like to ensure that my applications are interacting with I18n/$localize appropriately (called the correct number of times, with correct parameters, etc.). This just prevent silly errors if someone accidentally changes a trans-unit ID or the base translations value.

What I've tried

I have tried to replace the global $localize function with a spy in test.ts and avoiding importing @angular/localize/init:

import Spy = jasmine.Spy;
import createSpy = jasmine.createSpy;

const _global: any = typeof global !== "undefined" && global;

_global.$localize = createSpy("$localize");

declare global {
  const $localize: Spy;
}

And then using the spied $localize in the tests (see :

describe("I18nLocalizeComponent", () => {
 let component: I18nLocalizeComponent;
 let fixture: ComponentFixture<I18nLocalizeComponent>;

  let mockI18n: Spy;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ I18nLocalizeComponent ],
    })
      .compileComponents();
  }));

  beforeEach(() => {
    $localize.calls.reset();
    $localize.and.returnValue("Hello World!);

    fixture = TestBed.createComponent(I18nLocalizeComponent);
    component = fixture.componentInstance;
  });

  it("should call $localize once", () => {
    expect($localize).toHaveBeenCalledTimes(1);
  });
});

The spy does work but tests will fail if the component, or another component, uses the i18n directives in it's template, for example (I18nLocalizeTemplateComponent):

<p i18n>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aenean consequat.</p>

This will fail with the following error:

TypeError: Cannot read property 'substr' of undefined
        at <Jasmine>
        at removeInnerTemplateTranslation (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:34560:1)
        at getTranslationForTemplate (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:34582:1)
        at i18nStartFirstPass (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:34771:1)
        at ɵɵi18nStart (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:34718:1)
        at ɵɵi18n (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:35450:1)
        at I18nLocalizeTemplateComponent_Template (ng:///I18nLocalizeTemplateComponent.js:15:9)
        at executeTemplate (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:11949:1)
        at renderView (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:11735:1)
        at renderComponent (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:13244:1)
        at renderChildComponents (http://localhost:9877/_karma_webpack_/node_modules/@angular/core/__ivy_ngcc__/fesm2015/core.js:11538:1)
    Error: Expected undefined to be truthy.
        at <Jasmine>
        at UserContext.<anonymous> (http://localhost:9877/_karma_webpack_/src/app/i18n-localize-template/i18n-localize-template.component.spec.ts:23:23)
        at ZoneDelegate.invoke (http://localhost:9877/_karma_webpack_/node_modules/zone.js/dist/zone-evergreen.js:364:1)
        at ProxyZoneSpec.push../node_modules/zone.js/dist/zone-testing.js.ProxyZoneSpec.onInvoke (http://localhost:9877/_karma_webpack_/node_modules/zone.js/dist/zone-testing.js:292:1)

Does anyone have any advice on how to handle this use case or is it currently not supported? I haven't seen any documentation, tutorials or articles which help with this so any assistance would be greatly appreciated.

To recreate the issue above in the example repo you'd have to:

1. Uncomment code in test.ts
2. Comment out import from @angular/localize/init in polyfills.ts
3. Run tests for I18nLocalizeTemplateComponent

The tests could be executed by using npm run test -- --include src/app/i18n-localize-template/i18n-localize-template.component.spec.ts

Alternatively, use enable-localize-unit-tests branch then follow step 3.

Notes

1. The following has been added to polyfills.ts for the project as per Angular upgrade guide:

   import "@angular/localize/init";
   

2. I'm currently using Karma (4.4.1) and Jasmine (3.5.9) for unit testing

Environment details

     _                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 9.0.6
Node: 13.2.0
OS: darwin x64

Angular: 9.0.6
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, localize, platform-browser
... platform-browser-dynamic, router
Ivy Workspace: Yes

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.900.6
@angular-devkit/build-angular      0.900.6
@angular-devkit/build-ng-packagr   0.900.6
@angular-devkit/build-optimizer    0.900.6
@angular-devkit/build-webpack      0.900.6
@angular-devkit/core               9.0.6
@angular-devkit/schematics         9.0.6
@angular/cdk                       9.1.3
@ngtools/webpack                   9.0.6
@schematics/angular                9.0.6
@schematics/update                 0.900.6
ng-packagr                         9.0.3
rxjs                               6.5.4
typescript                         3.7.5
webpack                            4.41.2

Solution

The solution that I found was to spy on the translate function of $localize rather than $localize itself: test.ts

const _global: any = typeof global !== "undefined" && global;
const defaultFakedLocalizeTranslate: (messageParts: TemplateStringsArray,
                                      substitutions: readonly any[]) => [TemplateStringsArray, readonly any[]] =
  (messageParts: TemplateStringsArray, substitutions: readonly any[]) => [messageParts, substitutions];

_global.mockLocalize = createSpy("mockLocalize") as Spy;

declare global {
  const mockLocalize: Spy;
}

$localize.translate = mockLocalize.and.callFake(defaultFakedLocalizeTranslate);

Make sure you have imported @angular/localize/init in test.ts.

The I18nLocalizeComponent unit tests can be updated as follows:

describe('I18nLocalizeComponent', () => {
  let component: I18nLocalizeComponent;
  let fixture: ComponentFixture<I18nLocalizeComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ I18nLocalizeComponent ],
    })
      .compileComponents();
  }));

  beforeEach(() => {
    mockLocalize.calls.reset();

    fixture = TestBed.createComponent(I18nLocalizeComponent);
    component = fixture.componentInstance;
  });

  it('should call $localize once', () => {
    expect(mockLocalize).toHaveBeenCalledTimes(1);
  });
});

This change will also allow unit tests of component's with i18n tags in the template to run successfully as well.

To check out the changes see the fix-localize-unit-tests branch of the example repo.

Answered By - ross-moug