I tried to follow this thread but it I keep getting an error.

transform-response.interceptor.ts:

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { ApiResponseInterface } from '@walletxp/shared-interfaces';

@Injectable()
export class TransformResponseInterceptor<T>
  implements NestInterceptor<T, ApiResponseInterface<Record<string, unknown>>>
{
  intercept(context: ExecutionContext, next: CallHandler): Observable<ApiResponseInterface<Record<string, unknown>>> {
    return next.handle().pipe(map((data) => ({ success: true, data })));
  }
}

and for it's test, transform-response.interceptor.spec.ts:

import { TransformResponseInterceptor } from './transform-response.interceptor';
const interceptor = new TransformResponseInterceptor();

const executionContext: any = {
  switchToHttp: jest.fn().mockReturnThis(),
  getRequest: jest.fn().mockReturnThis(),
};

const callHandler = {
  handle: jest.fn(),
};

describe('ResponseInterceptor', () => {
  it('should be defined', () => {
    expect(interceptor).toBeDefined();
  });
  describe('#intercept', () => {
    it('t1', async () => {
      (executionContext.switchToHttp().getRequest as jest.Mock<any, any>).mockReturnValueOnce({
        body: { data: 'mocked data' },
      });
      callHandler.handle.mockResolvedValueOnce('next handle');
      const actualValue = await interceptor.intercept(executionContext, callHandler);
      expect(actualValue).toBe('next handle');
      expect(executionContext.switchToHttp().getRequest().body).toEqual({
        data: 'mocked data',
        addedAttribute: 'example',
      });
      expect(callHandler.handle).toBeCalledTimes(1);
    });
  });
});

My goal would be to mock the data returned from the controller and check if after it goes through the interceptor it equals the formatted data that I want.

CodePudding user response：

I have tested my interceptors, using the calls to the application, more like an end to end test.

import { Test, TestingModule } from '@nestjs/testing';
import * as request from 'supertest';
import { INestApplication, HttpStatus } from '@nestjs/common';

import { EmulatorHeadersInterceptor } from '@LIBRARY/interceptors/emulator-headers.interceptor';

import { AppModule } from '@APP/app.module';

describe('Header Intercepter', () => {
    let app: INestApplication;

    afterAll(async () => {
        await app.close();
    });

    beforeAll(async () => {
        const moduleFixture: TestingModule = await Test.createTestingModule({
            imports: [AppModule],
        }).compile();

        app = moduleFixture.createNestApplication();
        app.useGlobalInterceptors(new EmulatorHeadersInterceptor());
        await app.init();
    });

    it('./test (PUT) should have the interceptor data', async () => {
        const ResponseData$ = await request(app.getHttpServer())
            .put('/test')
            .send();

        expect(ResponseData$.status).toBe(HttpStatus.OK);
        expect(ResponseData$.headers['myheader']).toBe('interceptor');
    });
});

My interceptor is adding a header field, but for your interceptor, you would replace the header interceptor I am using, with your interceptor. From there, you can test that the response contains what you want.

CodePudding user response：

If you're looking for a simple unit test, then you need to understand how RxJS works for asynchronous testing. Something like the following could work:

describe('ResponseInterceptor', () => {
  let interceptor: ResponseInterceptor;

  beforeEach(() => {
    interceptor = new ResponseInterceptor();
  });

  it('should map the data', (done) => {
    // this sets up a mock execution context (which you don't use so it's blank)
    // and a mock CallHandler that returns a known piece of data 'test data'
    const obs$ = interceptor.intercept({} as any, { handle: () => of('test data') });
    // this tests the observable, and calls done when it is complete
    obs$.subscribe({
      next: (val) => {
        expect(val).toEqual({ success: true, data: 'test data' })
      }),
      complete: () => done()
    })
  });

});