Mocking & E2E Tests

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You mock a repository with { provide: UserRepo, useValue: { findOne: jest.fn() } }. How do you make findOne return a user in one specific test?

javascript

const repo = moduleRef.get<UserRepo>(UserRepo) as jest.Mocked<UserRepo>;
repo.findOne.mockResolvedValue({ id: '1', name: 'Ada' });

const result = await service.getUser('1');
expect(result.name).toBe('Ada');

AReassign the whole provider inside the test

BUse jest.mock('UserRepo')

CEdit the useValue object literal at runtime

DCall repo.findOne.mockResolvedValue(user) (or mockReturnValue) on the retrieved mock before acting

To unit-test a CanActivate guard, what do you typically provide?

javascript

import { ExecutionContext } from '@nestjs/common';

const context = {
  switchToHttp: () => ({ getRequest: () => ({ headers: { authorization: 'Bearer ok' } }) }),
} as unknown as ExecutionContext;

expect(guard.canActivate(context)).toBe(true);

AA real HTTP request from a browser

BNothing; guards can't be unit-tested

CA mocked ExecutionContext whose switchToHttp().getRequest() returns a crafted request object

DA full Nest application bootstrapped with app.listen()

How do you test a custom PipeTransform?

javascript

import { ArgumentMetadata, BadRequestException } from '@nestjs/common';

const meta: ArgumentMetadata = { type: 'body', metatype: String, data: '' };
expect(pipe.transform('42', meta)).toBe(42);
expect(() => pipe.transform('nope', meta)).toThrow(BadRequestException);

AInstantiate the pipe and call pipe.transform(value, metadata) directly, asserting the transformed value or thrown error

BRegister it globally and send HTTP requests only

CPipes are internal and cannot be invoked directly

DReplace it with a guard

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