Mock function under router in Node js - node.js

Question

Please consider the following scenario, but I could not solve it. A class are called under the router("/"). I would like to test router ("/") call and mock myFunc result.
class A {
myFunc = async () => {
await ...
return result
}
}
Controller file - C:
router.get("/", async (req, res) => {
var a = new A();
a.myFunc()
.then(result => {
res.json({"message": result});
}).catch(e => {
return []
})
});
C.test.js:
const request = require("supertest");
const app = require("../C");
jest.mock('A');
test("Test route /", async done => {
const myFuncMock = jest.fn().mockImplementation(() => [...]);
A.prototype.myFunc = myFuncMock;
await request(app)
.get("/")
.then(res => {
expect(res.status).toBe(200); // Not asserted
});
done()
});
I could not success to mock function results under the router.

Answer 1

Here is the integration test solution:
app.js:
const express = require('express');
const { Router } = require('express');
const A = require('./a');
const app = express();
const router = Router();
router.get('/', async (req, res) => {
const a = new A();
a.myFunc()
.then((result) => {
res.json({ message: result });
})
.catch((e) => {
return [];
});
});
app.use(router);
module.exports = app;
a.js:
class A {
myFunc = async () => {
const result = await 'real data';
return result;
};
}
module.exports = A;
app.test.js:
const app = require('./app');
const request = require('supertest');
const A = require('./a');
jest.mock('./a', () => {
const mA = { myFunc: jest.fn() };
return jest.fn(() => mA);
});
describe('61505692', () => {
afterEach(() => {
jest.clearAllMocks();
});
it('should pass', () => {
const mA = new A();
mA.myFunc.mockResolvedValueOnce('fake result');
return request(app)
.get('/')
.then((res) => {
expect(res.status).toBe(200);
});
});
});
integration test results with coverage report:
PASS stackoverflow/61505692/app.test.js (11.834s)
61505692
✓ should pass (34ms)
----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files | 92.31 | 100 | 75 | 91.67 |
app.js | 92.31 | 100 | 75 | 91.67 | 16
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 13.785s