How to stub async module dependencies for jest - node.js

Question

Let's say I have the following route:
import {example} from '../some/place'
const processRequest = async (req: Request, res: Response, next: NextFunction): Promise<void> => {
try {
console.log('in route handler')
const foo = await example(req.body.someData)
res.status(200).send()
} catch (e) {
next(e)
}
}
export { processRequest }
And then I write a test like so:
import * as exampleModule from '../some/place'
import { processRequest } from '../routes/processRequest'
import sinon from 'sinon'
sinon.stub(exampleModule, 'example').returns(new Promise(() => {
return someData
})
describe('example test', () => {
it('example test', async () => {
await processRequest(mockRequest, mockResponse, mockNext)
})
})
This fails with:
thrown: "Exceeded timeout of 5000 ms for a test.
Use jest.setTimeout(newTimeout) to increase the timeout value, if this is a long-running test."
Through console.logs, I have verified the following:
The original implementation of example is not called
ProcessRequest is called and prints to console
The line in the route after const foo = await example(req.body.someData) is never called and nothing is printed, suggesting that somehow the promise return from my stub is incorrect. For the life of me I do not know how.
Any advice on the best way to stub async dependencies for jest tests would be super welcome!

Answer 1

An working example:
processRequest.ts:
import { NextFunction, Response, Request } from 'express';
import { example } from './someplace';
const processRequest = async (req: Request, res: Response, next: NextFunction): Promise<void> => {
try {
console.log('in route handler');
const foo = await example(req.body.someData);
console.log('foo: ', foo);
res.status(200).send();
} catch (e) {
next(e);
}
};
export { processRequest };
someplace.ts:
export const example = async (arg) => 'real data';
processRequest.test.ts:
import * as exampleModule from './someplace';
import { processRequest } from './processRequest';
import type { Response, Request } from 'express';
import sinon from 'sinon';
describe('example test', () => {
it('example test', async () => {
const exampleStub = sinon.stub(exampleModule, 'example').resolves('test data');
const mockRequest = {
body: { someData: 'a' },
};
const mockResponse = {
status: sinon.stub().returnsThis(),
send: sinon.stub(),
};
const mockNext = sinon.stub();
await processRequest((mockRequest as unknown) as Request, (mockResponse as unknown) as Response, mockNext);
sinon.assert.calledWithExactly(exampleStub, 'a');
sinon.assert.calledWithExactly(mockResponse.status, 200);
sinon.assert.calledOnce(mockResponse.send);
});
});
Test result:
PASS stackoverflow/74944946/processRequest.test.ts (7.98 s)
example test
✓ example test (16 ms)
console.log
in route handler
at stackoverflow/74944946/processRequest.ts:6:13
console.log
foo: test data
at stackoverflow/74944946/processRequest.ts:8:13
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 8.442 s, estimated 9 s
package versions:
"jest": "^26.6.3",
"sinon": "^15.0.1",