EDIT 2: See the below comments

I am trying to write some tests for a middleware function, but cannot figure out how to write it so that .toHaveBeenCalled() matches the expected number of calls (in this case 1) instead of 0 calls. I currently create a variable within the test to mock an Express Response object, and pass that into the function I am testing:

index.ts

const doSomething = async (req, res) => {
  ....
  
  axios(options)
    .then((response) => {
        const data = response.data;

        ...

        res.status(200);
        res.send();
  ....

}

index.test.ts

const sampleResponse = {
  status: jest.fn(),
  send: jest.fn(),
  json: jest.fn(),
} as unknown as Response;

...

await doSomething(sampleRequest, sampleResponse);
expect(sampleResponse.status).toHaveBeenCalled();

Jest shows the lines with res.status(200) and res.send() as covered in the coverage report.

I have read some threads where this error has to do with different/distinct instances of mock functions being created when executing the test; is that the case here? Should I perhaps be testing for something entirely different (the function currently does not return anything)?

Edit:

I have pivoted to trying to test a side effect; I feel like I am close but am still getting 0 calls for this test too. I suspect it is the same issue regarding references/instances.

index.ts

import Foo from './foo.ts';

const doSomething = async (req, res) => {
  ....

  axios(options)
    .then((response) => {
        const data = response.data;

        ...
        // getInstance() looks for an instance and creates one if not defined
        Foo.getInstance().doFooThings();
    })
  ....

}

index.test.ts

import Foo from './foo.ts'

  ...
const fooMock = jest.spyOn(foo.prototype,'doFooThings').mockImplementation(() => Promise.resolve(console.log('hi')));
await doSomething(req, res);
expect(fooMock).toHaveBeenCalled(); // still says 0 calls, but 'hi' is getting console logged...
  ...