Advanced Testing

Preview — 3 of 10 questions

To unit-test an interceptor's intercept(context, next), what do you pass as next?

javascript

import { of } from 'rxjs';
import { CallHandler, ExecutionContext } from '@nestjs/common';

const next: CallHandler = { handle: () => of({ raw: true }) };
const context = {} as ExecutionContext;

interceptor.intercept(context, next).subscribe((result) => {
  expect(result).toEqual({ data: { raw: true } }); // after a wrapping interceptor
});

AA mock CallHandler whose handle() returns an observable, e.g. { handle: () => of(value) }

BThe real route handler from the controller

CA Promise that resolves to the value

Dnull, because interceptors don't use next

What does an exception filter test need to mock on ArgumentsHost?

javascript

import { ArgumentsHost, HttpException } from '@nestjs/common';

const json = jest.fn();
const status = jest.fn().mockReturnValue({ json });
const host = {
  switchToHttp: () => ({ getResponse: () => ({ status }), getRequest: () => ({ url: '/x' }) }),
} as unknown as ArgumentsHost;

filter.catch(new HttpException('Nope', 400), host);
expect(status).toHaveBeenCalledWith(400);

AswitchToHttp() returning getResponse()/getRequest() so you can assert the filter sets the right status and JSON body

BswitchToWs() only

CThe Prisma client

DThe Jest config object

What is a clean way to mock a Repository<Entity> for a service test?

javascript

import { getRepositoryToken } from '@nestjs/typeorm';
import { createMock } from '@golevelup/ts-jest';
import { Repository } from 'typeorm';

const moduleRef = await Test.createTestingModule({
  providers: [
    UserService,
    { provide: getRepositoryToken(User), useValue: createMock<Repository<User>>() },
  ],
}).compile();

AConnect to the real database in unit tests

BUse @golevelup/ts-jest's createMock<Repository<Entity>>() (or a manual object of jest.fn()s) and bind it via getRepositoryToken(Entity)

CSubclass Repository and override every method by hand each test

DPass undefined and hope the service handles it

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