fakeAsync not waiting for async operation to complete

Question

Context

I'm testing a component which is using an observable-based service to get some data and show it for i18n purpose.

The i18n service is custom because of a specific need.

The component works in dev mode (used in some templates, works fine) but the test fails.

Source

Component

@Component({
    selector     : "i18n",
    template     : '<span [innerHTML]="text"></span><span #wrapper hidden="true"><ng-content></ng-content><span>',
    encapsulation: ViewEncapsulation.None
})
export class I18nComponent implements OnChanges {

    constructor(private i18n:I18n) {
    }

    @ViewChild('wrapper')
    content:ElementRef;

    @Input('key')
    key:string;

    @Input('domain')
    domain:string;

    @Input('variables')
    variables:Variables = [];

    @Input("plural")
    plural:number;

    text:string;

    ngOnChanges():any {
        this.i18n.get(this.key, this.content.nativeElement.innerHTML, this.variables, this.domain).subscribe((res) => {
            this.text = res;
        });
    }
}

I18n.get

public get(key:string,
               defaultValue?:string,
               variables:Variables = {},
               domain?:string):Observable<string>{
    const catalog = {
                         "StackOverflowDomain":
                         {
                             "my-key":"my-value"
                         }
                    };

    return Observable.of(catalog[domain][key]).delay(300);
}

with Variables:

export interface Variables {
    [key:string]:any;
}

The test

describe("I18n component", () => {

    beforeEach(() => {
        TestBed.configureTestingModule({
            providers   : [
                I18n,
                {
                    provide : I18N_CONFIG,
                    useValue: {
                        defaultLocale : "fr_FR",
                        variable_start: '~',
                        variable_end  : '~'
                    }
                },
                {
                    provide : I18N_LOADERS,
                    useClass: MockLocaleLoader,
                    multi   : true
                }
            ],
            declarations: [
                I18nComponent
            ]
        });
        fixture = TestBed.createComponent<I18nComponent>(I18nComponent);
        comp = fixture.componentInstance;
    });

    fit("can call I18n.get.", fakeAsync(() => {
        comp.content.nativeElement.innerHTML = "nope";
        comp.key = "test";
        comp.domain = "test domain";
        comp.ngOnChanges();
        tick();
        fixture.detectChanges();
        expect(comp.text).toBe("test value");
    }));

});

Problem

The test fails with message :

Expected undefined to be 'test value'.

Error: 1 periodic timer(s) still in the queue.

Because i18n.get did not finish its work before assertion has been checked, so comp.text is still undefined.

Already tried

• Adding an very high value in tick method call, changed nothing (tried with 5000).
• Make ngOnChanges return a Promise<void> that resolves right after this.text = res; and change fakeAsync zone for a simple test using a done method caled in then of comp.ngOnChanges. It works, but ngOnChanges should not return a Promise and I want a clean solution.

Answer 1

Note that async and fakeasync are not as powerful and inclusive as jasmine.done

Taking the exact note from (at the time of this writing): https://angular.io/guide/testing#component-fixture

It says:

Writing test functions with done, while more cumbersome than async and fakeAsync, is a viable and occasionally necessary technique. For example, you can't call async or fakeAsync when testing code that involves the intervalTimer, as is common when testing async Observable