How to test function in class using jest - node.js

Question

I wasn't able to make unit testing worked using jest
I'm trying to test a specific function that's calling or expecting result from other function but I'm not sure why it is not working. I'm pretty new to unit testing and really have no idea how could I make it work. currently this is what I've tried
export class OrganizationService {
constructor() {
this.OrganizationRepo = new OrganizationRepository()
}
async getOrganizations(req) {
if (req.permission !== 'internal' && req.isAuthInternal === false) {
throw new Error('Unauthenticated')
}
const opt = { deleted: true }
return this.OrganizationRepo.listAll(opt)
}
}
This is my OrganizationRepository that extends the MongoDbRepo
import { MongoDbRepo } from './mongodb_repository'
export class OrganizationRepository extends MongoDbRepo {
constructor(collection = 'organizations') {
super(collection)
}
}
and this is the MongoDbRepo
const mongoClient = require('../config/mongo_db_connection')
const mongoDb = require('mongodb')
export class MongoDbRepo {
constructor(collectionName) {
this.collection = mongoClient.get().collection(collectionName)
}
listAll(opt) {
return new Promise((resolve, reject) => {
this.collection.find(opt).toArray((err, data) => {
if (err) {
reject(err)
}
resolve(data)
})
})
}
}
and this is the test that I've made
import { OrganizationService } from '../../../src/services/organization_service'
describe('getOrganizations', () => {
it('should return the list of organizations', () => {
// const OrgRepo = new OrganizationRepository()
const orgService = new OrganizationService()
const OrgRepo = jest.fn().mockReturnValue("[{_id: '123', name: 'testname'}, {_id: '456, name: 'testname2'}]")
// orgService.getOrganizations = jest.fn().mockReturnValue('')
const result = orgService.getOrganizations()
expect(result).toBe(OrgRepo)
})
})

Answer 1

I see two issues in the way you are testing:
1.
You are trying to test an asynchronous method, and on your test, you are not waiting for this method to be finished before your expect statement.
A good test structure should be:
it('should test your method', (done) => {
const orgService = new OrganizationService();
const OrgRepo = jest.fn().mockReturnValue("[{_id: '123', name: 'testname'}, {_id: '456, name: 'testname2'}]")
orgService.getOrganizations()
.then((result) => {
expect(result).toEqual(OrgRepo); // I recommend using "toEqual" when comparing arrays
done();
});
})
Don't forget to put done as a parameter for your test!
You can find more about testing asynchronous functions on the Jest official documentation.
2.
In order to test your method properly, you want to isolate it from external dependencies. Here, the actual method OrganizationRepo.listAll() is called. You want to mock this method, for instance with a spy, so that you control its result and only test the getOrganizations method. That would look like this:
it('should test your method', (done) => {
const req = {
// Whatever structure it needs to be sure that the error in your method is not thrown
};
const orgService = new OrganizationService();
const orgRepoMock = spyOn(orgService['OrganizationRepo'], 'listAll')
.and.returnValue(Promise.resolve("[{_id: '123', name: 'testname'}, {_id: '456, name: 'testname2'}]"));
const OrgRepo = jest.fn().mockReturnValue("[{_id: '123', name: 'testname'}, {_id: '456, name: 'testname2'}]");
orgService.getOrganizations(req)
.then((result) => {
expect(result).toEqual(OrgRepo); // I recommend using "toEqual" when comparing arrays
expect(orgRepoMock).toHaveBeenCalled(); // For good measure
done();
});
})
This way, we make sure that your method is isolated and its outcome cannot be altered by external methods.
For this particular method, I also recommend that you test the error throwing depending on the input of your method.

Answer 2

I was able to answer this, first is I mocked the repository using
jest.mock('path/to/repo')
const mockGetOne = jest.fn()
OrganizationRepository.protorype.getOne = mockGetOne
then the rest is the test