advanced patterns When Testing Asynchronous Functions in Angular Using Jasmine
I'm integrating two systems and I'm working on a personal project and I'm working with an scenario while testing asynchronous functions in my Angular application with Jasmine..... I have a service that fetches data from an API and processes it before returning the result. The question arises when I try to test this asynchronous behavior; the test completes before the promise resolves, leading to unexpected results. Here is a simplified version of my service and the test: ```typescript // data.service.ts import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { Observable } from 'rxjs'; import { map } from 'rxjs/operators'; @Injectable({ providedIn: 'root' }) export class DataService { constructor(private http: HttpClient) { } fetchData(): Observable<any> { return this.http.get('https://api.example.com/data').pipe( map(response => { // Process the data return response; }) ); } } ``` And here’s how I'm trying to test it: ```typescript // data.service.spec.ts import { TestBed } from '@angular/core/testing'; import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing'; import { DataService } from './data.service'; describe('DataService', () => { let service: DataService; let httpMock: HttpTestingController; beforeEach(() => { TestBed.configureTestingModule({ imports: [HttpClientTestingModule], providers: [DataService] }); service = TestBed.inject(DataService); httpMock = TestBed.inject(HttpTestingController); }); afterEach(() => { httpMock.verify(); }); it('should fetch and process data', (done) => { const mockResponse = { data: 'test data' }; service.fetchData().subscribe(result => { expect(result).toEqual(mockResponse); done(); // This is where I think the scenario might be }); const req = httpMock.expectOne('https://api.example.com/data'); expect(req.request.method).toBe('GET'); req.flush(mockResponse); }); }); ``` When I run this test, I get an behavior that states `Expected undefined to equal { data: 'test data' }`. It seems like the subscription might be resolving before the mock response is flushed, despite using `done()` to signal completion. I've tried moving the `done()` call to different locations within the subscription, but that hasn't changed the outcome. Does anyone have insights into correctly handling this asynchronous behavior in Jasmine tests? Am I missing something in how Jasmine waits for the promises to resolve? The stack includes Typescript and several other technologies. Could this be a known issue? Thanks for taking the time to read this!