What are some effective strategies for achieving comprehensive test coverage when unit testing NestJs http requests?

Question

What are some effective strategies for achieving comprehensive test coverage when unit testing NestJs http requests?

I am facing an issue with testing my NestJs Service. I have a method that performs a GET http request:

getEntries(): Observable<Entries[]> {
    Logger.log(`requesting GET: ${this.apiHost}${HREF.entries}`);
    return this.http.get(`${this.apiHost}${HREF.entries}`).pipe(
      catchError((error) => {
        return throwError(error);
      }),
      map(response => response.data)
    );
  }

I am trying to write a unit test for this method in order to cover all lines of code. Despite using the "nock" package to mock the http request, I am unable to improve the coverage result.

return throwError(error);

map(response => response.data);

These two lines remain uncovered.

Below is my test file:

describe('getEntries method', () => {
    it('should perform a get request and return entries', () => {
      nock('http://localhost:3000')
        .get('/v1/entries')
        .reply(200, {
          data: require('../mocks/entries.json')
        });
      try {
        const result = service.getEntries();
        result.subscribe(res => {
          expect(res).toEqual(require('../mocks/entries.json'));
        });
      } catch (e) {
        expect(e).toBeUndefined();
      }
    });
    it('should return an error if the request fails', () => {
      nock('http://localhost:3000')
        .get('/v1/entries')
        .replyWithError('request failed');
      service.getEntries().subscribe(res => {
        expect(res).toBeUndefined();
      }, err => {
        expect(err).toBe('request failed');
      })
    });
  });

typescript unit-testing jestjs nestjs

Answer 1

Answer №1

Although I have not previously utilized nock, a simple way to specify the response for HttpService using jest.spyOn. It is essential to remember that the return value is synchronous since it returns an observable. To test the positive scenario, you can try something like this:

it('should perform the request and retrieve the entries', (done) => {
  const httpSpy = jest.spyOn(httpService, 'get')
    .mockReturnValue(of({data: require('../mocks/entries.json')}))
  let data = {};
  service.getEntires().subscribe({
    next: (val) => {data = val},
    error: (err) => { throw error; }
    complete: () => {
      expect(data).toEqual(require('../mocks/entries.json'))
      done();
    }
});

Similarly, for handling errors, you can utilize the throwError() operator.

Both of and throwError are imported from rxjs. One thing worth noting is that in this approach, you need to access the HttpService from the current module context, similar to obtaining any other service. This distinction is important to highlight.

Answer 2

Although I have not previously utilized nock, a simple way to specify the response for HttpService using jest.spyOn. It is essential to remember that the return value is synchronous since it returns an observable. To test the positive scenario, you can try something like this:

it('should perform the request and retrieve the entries', (done) => {
  const httpSpy = jest.spyOn(httpService, 'get')
    .mockReturnValue(of({data: require('../mocks/entries.json')}))
  let data = {};
  service.getEntires().subscribe({
    next: (val) => {data = val},
    error: (err) => { throw error; }
    complete: () => {
      expect(data).toEqual(require('../mocks/entries.json'))
      done();
    }
});

Similarly, for handling errors, you can utilize the throwError() operator.

Both of and throwError are imported from rxjs. One thing worth noting is that in this approach, you need to access the HttpService from the current module context, similar to obtaining any other service. This distinction is important to highlight.

Answer 3

Answer №2

Appreciate your response! The code is working at its core, but I had to tweak a few things for the testing phase. Check out the adjustments I made:

describe('getEntries method', () => {
    it('fetches entries through a get request and returns them', (done) => {
      jest.spyOn(service['http'], 'get').mockReturnValue(of({data: require('../mocks/entries.json'), status: 200, statusText: 'OK', headers: {}, config: {}}));
      let data = {};

      service.getEntries().subscribe({
        next: (val) => {data = val},
        error: (err) => { throw err; },
        complete: () => {
          expect(data).toEqual(require('../mocks/entries.json'))
          done();
        }
      });
    });
    it('returns an error if the request fails', (done) => {
      jest.spyOn(service['http'], 'get').mockReturnValue(throwError('request failed'));
      let data = {};

      service.getEntries().subscribe({
        next: (val) => {data = val},
        error: (err) => {
          expect(err).toBe('request failed');
          done();
        },
        complete: () => {
          expect(data).toBeUndefined();
          done();
        }
      });
    });
  });

I included 'status', 'statusText', 'header', 'config' while mocking AxiosResponse on httpSpy mockReturnValue to avoid any type errors.

In the second part, I initially spied on the httpService like this:

let httpService: HttpService;
httpService = module.get(HttpService)

Turns out that approach wasn't effective. Instead, I needed to spy on the HttpService injection within my Service.

constructor(private readonly http: HttpService) {}

So now my spy looks like: service['http']. With these adjustments, I've achieved full coverage on this http request :)

Thanks a bunch for your help! Enjoy the rest of your day!

Answer 4

Appreciate your response! The code is working at its core, but I had to tweak a few things for the testing phase. Check out the adjustments I made:

describe('getEntries method', () => {
    it('fetches entries through a get request and returns them', (done) => {
      jest.spyOn(service['http'], 'get').mockReturnValue(of({data: require('../mocks/entries.json'), status: 200, statusText: 'OK', headers: {}, config: {}}));
      let data = {};

      service.getEntries().subscribe({
        next: (val) => {data = val},
        error: (err) => { throw err; },
        complete: () => {
          expect(data).toEqual(require('../mocks/entries.json'))
          done();
        }
      });
    });
    it('returns an error if the request fails', (done) => {
      jest.spyOn(service['http'], 'get').mockReturnValue(throwError('request failed'));
      let data = {};

      service.getEntries().subscribe({
        next: (val) => {data = val},
        error: (err) => {
          expect(err).toBe('request failed');
          done();
        },
        complete: () => {
          expect(data).toBeUndefined();
          done();
        }
      });
    });
  });

I included 'status', 'statusText', 'header', 'config' while mocking AxiosResponse on httpSpy mockReturnValue to avoid any type errors.

In the second part, I initially spied on the httpService like this:

let httpService: HttpService;
httpService = module.get(HttpService)

Turns out that approach wasn't effective. Instead, I needed to spy on the HttpService injection within my Service.

constructor(private readonly http: HttpService) {}

So now my spy looks like: service['http']. With these adjustments, I've achieved full coverage on this http request :)

Thanks a bunch for your help! Enjoy the rest of your day!

What are some effective strategies for achieving comprehensive test coverage when unit testing NestJs http requests?

Answer №1

Answer №2

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