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Mock uuid in jest - uuid called in service function

I have a jest test that is calling the real function and it compares the result returned with an expected result. The service function called uses uuid. I have all kind of errors while trying to mock uuid and can't seem to succeed.
My code is:
import uuid from 'uuid';
import tinyRuleset from './tiny_ruleset.json';
import { Store } from '../store';
describe('TuningStore test ', () => {
let store;
let db;
beforeEach(async () => {
db = levelup(encode(memdown(), { valueEncoding: 'json' }));
store= new Store(db);
});
test('createObject()', async () => {
jest.spyOn(uuid, 'v4').mockReturnValue('abc22');
const obj = await store.createObject();
expect(obj ).toEqual({
a: expect.any(string),
b: 'tiny_ruleset',
v: expect.any(Function)
});
});
})
I tried several ways, but none of them worked. My current error is: uuid is not a function. Also tried this:
const uuidv4Spy = jest.spyOn(store.$uuid, 'v4').mockReturnValueOnce('fake uuid');
Basically uuid is used inside the store.createObject() function.
Thank you!

As explained here Mock uuid
const uuidMock = jest.fn().mockImplementation(() => {
return 'my-none-unique-uuid';
});
jest.mock('uuid', () => {
return uuidMock;
});
you need to apply the mock in the test file before you are importing your real file.

Mock Service Worker / Node isn't working and I can't see why

If anyone can spot whatever's wrong with this code, I'd really appreciate. Not seeing an issue myself, but it's failing.
import React from "react"
import {setupServer} from "msw/node"
import {rest} from "msw"
describe("mocking apis", () => {
const testCall = jest.fn()
const server = setupServer(
...[
rest.get("/test", (req, res, ctx) => {
console.log('This line is never run')
testCall()
return res(ctx.json({message: "success"}))
}),
]
)
test("test", async () => {
server.listen()
fetch("/test", {method: "GET"})
expect(testCall).toHaveBeenCalled()
server.close();
})
})

I also had this problem. After a while I realized the cause. In my src/setupTests.js file I had:
import { enableFetchMocks } from 'jest-fetch-mock';
...
enableFetchMocks();
So, fetch() was not being called at all.
I made 3 changes to the posted code to get it to work:
Import and call disableFetchMocks().
Add await before fetch(....
Change the URL to http://localhost/test, to address a test error that said I needed to use an absolute URL.
Here is the working code (cleaned up to AirB&B style by PyCharm):
import { setupServer } from 'msw/node';
import { rest } from 'msw';
import { disableFetchMocks } from 'jest-fetch-mock';
describe('mocking apis', () => {
const testCall = jest.fn();
const server = setupServer(
...[
rest.get('http://localhost/test', (req, res, ctx) => {
console.log('This line is run');
testCall();
return res(ctx.json({ message: 'success' }));
}),
],
);
test('test', async () => {
disableFetchMocks();
server.listen();
await fetch('http://localhost/test', { method: 'GET' });
expect(testCall).toHaveBeenCalled();
server.close();
});
});

When you run your tests these run in a node environment, in this fetch function does not exist (it means: global.fetch) for that reason you need to make a polyfill.
I recommend installing the npm package 'whatwg-fetch'
npm install whatwg-fetch
and use it like this:
import 'whatwg-fetch';
This video could help

How to mock a method inside Express router Jest test?

I'm trying to test a router in Node.js app with Jest + Supertest, but my router is making a call to service, which is calling the endpoint:
router.post('/login', async (req, res, next) => {
try {
const { username, password } = req.body;
// I WANT TO MOCK userService.getUserInfo FUNCTION, BECAUSE IT IS MAKING A POST CALL
const identity = await userService.getUserInfo(username, password);
if (!identity.authenticated) {
return res.json({});
}
const requiredTenantId = process.env.TENANT_ID;
const tenant = identity.tenants.find(it => it.id === requiredTenantId);
if (requiredTenantId && !tenant) {
return res.json({});
}
const userResponse = {
...identity,
token: jwt.sign(identity, envVars.getVar(envVars.variables.AUTH_TOKEN_SECRET), {
expiresIn: '2h',
}),
};
return res.json(userResponse);
} catch (err) {
return next(err);
}
});
This is my test that works well:
test('Authorized - respond with user object', async () => {
const response = await request(app)
.post('/api/user/login')
.send(users.authorized);
expect(response.body).toHaveProperty('authenticated', true);
});
this is how getUserInfo function looks like:
const getUserInfo = async (username, password) => {
const identity = await axios.post('/user', {username, password});
return identity;
}
but it executes the method getUserInfo inside a router and this method is making a REST call - I want to mock this method in order to avoid REST calls to other services.
How it could be done?
I've found a mockImplementation function in Jest docs https://jestjs.io/docs/en/mock-function-api.html#mockfnmockimplementationfn
but how I can mock func inside a supertest testing?

You can use jest's auto mocking at the top of your test
like so:
jest.mock('./path/to/userService');
// and include it as well in your test
const userService = require('./path/to/userService');
it will generate a mock of the entire module and every function will be replaced with jest.fn() with no implementation
and then depending on the userService if it's just an object it's getUserInfo method will be a jest.fn() and you can set it's return value like this:
// resolved value as it should return a promise
userService.getUserInfo.mockResolvedValue(mockIdentity);
and the mockIdentity will have to look something like this:
const mockIdentity = {
authenticated: true,
tenants: [
{
id: "x12",
mockInfo: "mock-info-value"
}
],
mother: "Superwoman",
father: "Superman"
})
}

Jest - mock a named class-export in typescript

I have a node module which exports a few classes, one of which is Client, which I use to create a client (having a few APIs as methods).
I'm trying to test my module which uses this node module as a dependency using Jest. However, I've been unable to successfully mock the one method (say search()) in the Client class.
Here is my spec for myModule:
//index.spec.ts
import * as nock from 'nock';
import * as externalModule from 'node-module-name';
import { createClient } from './../../src/myModule';
describe(() => {
beforeAll(() => {
nock.disableNetConnect();
});
it('test search method in my module', () => {
jest.mock('node-module-name');
const mockedClient = <jest.Mock<externalModule.Client>>externalModule.Client;
const myClient = createClient({/*params*/}); //returns instance of Client class present in node module by executing Client() constructor
myClient.searchByName('abc'); //calls search API - I need to track calls to this API
expect(mockedClient).toHaveBeenCalled();
expect(mockedClient.prototype.search).toHaveBeenCalledWith('abc');
});
});
This, however, doesn't create a mock at all and triggers a nock error since the search API tries to connect to the url (given through params).
I've also tried mocking the Client class like the following. While successfully creating a mock for the Client class and also the search API (verified that search() is also mocked through console logs), it gives me an error while I try to check if search() has been called.
externalModule.Client = jest.fn(() => { return { search: jest.fn(() => Promise.resolve('some response')) } });
//creates the mock successfully, but not sure how to track calls to 'search' property
const client = myModule.createClient(/*params*/);
client.searchByName('abc');
expect(externalModule.Client).toHaveBeenCalled(); //Successful
expect(externalModule.Client.prototype.search).toHaveBeenCalled(); //returns error saying "jest.fn() value must be a mock function or spy, Received: undefined"
I'm not sure what I'm doing wrong. Thank you in advance.

Mocking whole module
Try moving jest.mock to the top of file
//index.spec.ts
const search = jest.fn();
jest.mock('node-module-name', () => ({
Client: jest.fn(() => ({ search }))
}));
import * as nock from 'nock';
import * as externalModule from 'node-module-name';
import { createClient } from './../../src/myModule';
describe(() => {
beforeAll(() => {
nock.disableNetConnect();
});
it('test search method in my module', () => {
const myClient = createClient({/*params*/});
myClient.searchByName('abc');
expect(externalModule.Client).toHaveBeenCalled();
expect(search).toHaveBeenCalledWith('abc');
externalModule.Client.mockClear();
search.mockClear();
});
});
Mocking only Client
Create search constant and track it.
const search = jest.fn();
externalModule.Client = jest.fn(() => ({ search }));
const client = myModule.createClient(/*params*/);
client.searchByName('abc');
expect(externalModule.Client).toHaveBeenCalled();
expect(search).toHaveBeenCalled();

Here is how I mocked it. I had to change naming and removing some code to avoid exposing original source.
jest.mock('../foo-client', () => {
return { FooClient: () => ({ post: mockPost }) }
})
Full code.
// foo-client.ts
export class FooClient {
constructor(private config: any)
post() {}
}
// foo-service.ts
import { FooClient } from './foo-client'
export class FooLabelService {
private client: FooClient
constructor() {
this.client = new FooClient()
}
createPost() {
return this.client.post()
}
}
// foo-service-test.ts
import { FooService } from '../foo-service'
const mockPost = jest.fn()
jest.mock('../foo-client', () => {
return { FooClient: () => ({ post: mockPost }) }
})
describe('FooService', () => {
let fooService: FooService
beforeEach(() => {
jest.resetAllMocks()
fooService = new FooService()
})
it('something should happened', () => {
mockPost.mockResolvedValue()
fooService.createPost()
})
})

How to connect to mongoDB and test for drop collection?

This is how I connect to a mongoDB using monk(). I'll store it in state.
Assume we want to drop some collections, we call dropDB.
db.js
var state = {
db: null
}
export function connection () {
if (state.db) return
state.db = monk('mongdb://localhost:27017/db')
return state.db
}
export async function dropDB () {
var db = state.db
if (!db) throw Error('Missing database connection')
const Users = db.get('users')
const Content = db.get('content')
await Users.remove({})
await Content.remove({})
}
I'm not quite sure if it is a good approach to use state variable. Maybe someone can comment on that or show an improvement.
Now I want to write a unit test for this function using JestJS:
db.test.js
import monk from 'monk'
import { connection, dropDB } from './db'
jest.mock('monk')
describe('dropDB()', () => {
test('should throw error if db connection is missing', async () => {
expect.assertions(1)
await expect(dropDB()).rejects.toEqual(Error('Missing database connection'))
})
})
This part is easy, but the next part gives me two problems:
How do I mock the remove() methods?
test('should call remove() methods', async () => {
connection() // should set `state.db`, but doesn't work
const remove = jest.fn(() => Promise.resolve({ n: 1, nRemoved: 1, ok: 1 }))
// How do I use this mocked remove()?
expect(remove).toHaveBeenCalledTimes(2)
})
And before that? How do I setup state.db?
Update
As explained by poke the global variable makes the problem. So I switched to a class:
db.js
export class Db {
constructor() {
this.connection = monk('mongdb://localhost:27017/db');
}
async dropDB() {
const Users = this.connection.get('users');
const Content = this.connection.get('content');
await Users.remove({});
await Content.remove({});
}
}
which results in this test file:
db.test.js
import { Db } from './db'
jest.mock('./db')
let db
let remove
describe('DB class', () => {
beforeAll(() => {
const remove = jest.fn(() => Promise.resolve({ n: 1, nRemoved: 1, ok: 1 }))
Db.mockImplementation(() => {
return { dropDB: () => {
// Define this.connection.get() and use remove as a result of it
} }
})
})
describe('dropDB()', () => {
test('should call remove method', () => {
db = new Db()
db.dropDB()
expect(remove).toHaveBeenCalledTimes(2)
})
})
})
How do I mock out any this elements? In this case I need to mock this.connection.get()

Having a global state is definitely the source of your problem here. I would suggest to look for a solution that does not involve global variables at all. As per Global Variables Are Bad, global variables cause tight coupling and make things difficult to test (as you have noticed yourself).
A better solution would be to either pass the database connection explicitly to the dropDB function, so it has the connection as an explicit dependency, or to introduce some stateful object that holds onto the connection and offers the dropDB as a method.
The first option would look like this:
export function openConnection() {
return monk('mongdb://localhost:27017/db');
}
export async function dropDB(connection) {
if (!connection) {
throw Error('Missing database connection');
}
const Users = connection.get('users');
const Content = connection.get('content');
await Users.remove({});
await Content.remove({});
}
This would also make it very easy to test dropDB as you can now just pass a mocked object for it directly.
The other option could look like this:
export class Connection() {
constructor() {
this.connection = monk('mongdb://localhost:27017/db');
}
async dropDB() {
const Users = this.connection.get('users');
const Content = this.connection.get('content');
await Users.remove({});
await Content.remove({});
}
}
A test for the first option could look like this:
test('should call remove() methods', async () => {
const usersRemove = jest.fn().mockReturnValue(Promise.resolve(null));
const contentRemove = jest.fn().mockReturnValue(Promise.resolve(null));
const dbMock = {
get(type) {
if (type === 'users') {
return { remove: usersRemove };
}
else if (type === 'content') {
return { remove: contentRemove };
}
}
};
await dropDB(dbMock);
expect(usersRemove).toHaveBeenCalledTimes(1);
expect(contentRemove).toHaveBeenCalledTimes(1);
});
Basically, the dropDB function expects an object that has a get method which when called returns an object that has a remove method. So you just need to pass something that looks like that, so the function can call those remove methods.
For the class, this is a bit more complicated since the constructor has a dependency on the monk module. One way would be to make that dependency explicit again (just like in the first solution), and pass monk or some other factory there. But we can also use Jest’s manual mocks to simply mock the whole monk module.
Note that we do not want to mock the module containing our Connection type. We want to test that, so we need it in its un-mocked state.
To mock monk, we need to create a mock module of it at __mocks__/monk.js. The manual points out that this __mocks__ folder should be adjacent to the node_modules folder.
In that file, we simply export our custom monk function. This is pretty much the same we already used in the first example, since we only care about getting those remove methods in place:
export default function mockedMonk (url) {
return {
get(type) {
if (type === 'users') {
return { remove: mockedMonk.usersRemove };
}
else if (type === 'content') {
return { remove: mockedMonk.contentRemove };
}
}
};
};
Note that this refers to the functions as mockedMonk.usersRemove and mockedMonk.contentRemove. We’ll use this in the test to configure those function explicitly during the test execution.
Now, in the test function, we need to call jest.mock('monk') to enable Jest to mock the monk module with our mocked module. Then, we can just import it too and set our functions within the test. Basically, just like above:
import { Connection } from './db';
import monk from 'monk';
// enable mock
jest.mock('./monk');
test('should call remove() methods', async () => {
monk.usersRemove = jest.fn().mockReturnValue(Promise.resolve(null));
monk.contentRemove = jest.fn().mockReturnValue(Promise.resolve(null));
const connection = new Connection();
await connection.dropDB();
expect(monk.usersRemove).toHaveBeenCalledTimes(1);
expect(monk.contentRemove).toHaveBeenCalledTimes(1);
});