How to mock async method with jest in nodejs - node.js

Question

I have below mentioned files
|_ utils.js
|_methods.js
I am doing unit testing for rest.js methods, file contents are
methods.js
import Express from 'express'
import { add_rec } from './utils'
export const create_rec = () => async (req: Express.Request, res: Express.Response) => {
const rec_body = req.body.rec
return add_rec(rec_body)
.then((ret) => res.status(201).send(ret))
.catch((e) => {
res.status(500).send({ message: e.message })
})
}
How can mock the add_rec async function so that I can unit-test my create_rec
function
I am trying to test create_rec below way but it is not allowing me to mock add_rec method
mport { getMockReq, getMockRes } from '#jest-mock/express'
import { add_rec } from './utils'
jest.mock('./utils')
describe('test create_rec method valid param', () => {
it('test create_rec method', async () => {
const req = getMockReq({
body: {
rec: {},
},
})
const { res } = getMockRes<any>({
status: jest.fn(),
send: jest.fn(),
})
add_rec.mockResolved({}) // this line is giving error in fact it is not mocked i think
await create_rec()(req, res)
expect(res.status).toHaveBeenCalledTimes(1)
expect(res.send).toHaveBeenCalledTimes(1)
})
})
Please help me with this.

Answer 1

Your code is almost correct, except that you need to do some processing on the TS type of the mock method, you can use type assertion.
E.g.
methods.ts:
import Express from 'express';
import { add_rec } from './utils';
export const create_rec = () => async (req: Express.Request, res: Express.Response) => {
const rec_body = req.body.rec;
return add_rec(rec_body)
.then((ret) => res.status(201).send(ret))
.catch((e) => {
res.status(500).send({ message: e.message });
});
};
utils.ts:
export async function add_rec(params): Promise<any> {
console.log('real implementation');
}
methods.test.ts:
import Express from 'express';
import { create_rec } from './methods';
import { add_rec } from './utils';
jest.mock('./utils');
describe('68419899', () => {
test('should pass', async () => {
(add_rec as jest.MockedFunction<any>).mockResolvedValueOnce({});
const req = ({ body: { rec: {} } } as unknown) as Express.Request;
const res = ({ status: jest.fn().mockReturnThis(), send: jest.fn() } as unknown) as Express.Response;
await create_rec()(req, res);
expect(add_rec).toBeCalledWith({});
expect(res.status).toBeCalledWith(201);
expect(res.send).toBeCalledWith({});
});
});
test result:
PASS examples/68419899/methods.test.ts (8.659 s)
68419899
✓ should pass (5 ms)
------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
------------|---------|----------|---------|---------|-------------------
All files | 81.82 | 100 | 66.67 | 75 |
methods.ts | 88.89 | 100 | 80 | 83.33 | 10
utils.ts | 50 | 100 | 0 | 50 | 2
------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 9.198 s