Jest tests - Please add 'import "reflect-metadata"' to the top of your entry point

Question

I'm developing an application using dependency injection with tsyringe. That's the example of a service that receives the repository as a dependency:

import { injectable, inject } from 'tsyringe'

import IAuthorsRepository from '@domains/authors/interfaces/IAuthorsRepository'

@injectable()
export default class ListAuthorsService {
  constructor (
    @inject('AuthorsRepository')
    private authorsRepository: IAuthorsRepository
  ) {}

And the dependencies container:

import { container } from 'tsyringe'

import IAuthorsRepository from '@domains/authors/interfaces/IAuthorsRepository'
import AuthorsRepository from '@domains/authors/infra/typeorm/repositories/AuthorsRepository'

container.registerSingleton<IAuthorsRepository>(
  'AuthorsRepository',
  AuthorsRepository
)

export default container

In the tests, I don't want to use the dependencies registered on the container, but instead, to pass a mock instance via parameter.

let authorsRepository: AuthorsRepositoryMock
let listAuthorsService: ListAuthorsService

describe('List Authors', () => {
  beforeEach(() => {
    authorsRepository = new AuthorsRepositoryMock()
    listAuthorsService = new ListAuthorsService(authorsRepository)
  })

But I'm receiving the following error:

tsyringe requires a reflect polyfill. Please add 'import "reflect-metadata"' to the top of your entry point.

What I thought was - "I may need to import the reflect-metadata package before executing the tests". So I created a jest.setup.ts which imports the reflect-metadata package. But another error occurs:

The instance of the repository is somehow undefined.

I would like to run my tests in peace.

Answer 1

First create in root of your project an jest.setup.ts.

In your jest.config.js, search for this line:

// A list of paths to modules that run some code to configure or set up the testing framework before each test
// setupFilesAfterEnv: [],

uncomment, and add your jest.setup.ts file path.

// A list of paths to modules that run some code to configure or set up the testing framework before each test
setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'],

Now import the reflect-metadata in jest.setup.ts:

import 'reflect-metadata';

And run tests again.