Can functions that are in a standalone node server be mocked without having to start a server in vitest?

[dsleandata]

Hello, i have a node server running in my local environment hosted on localhost:5000. I also have a vitest test running, where I want to test an /endpoint in the node server. There is a function in /endpoint that i want to mock, but it seems like the mock is not working and its calling the actual function. The function itself functionIWantToMock is async and returns a map after calling on a promise chain within it (which I want to avoid and want it to just return the map) Is this because vitest can't mock a function in a server not tied to it? any documentation i can read to understand this better? Or should I be mocking instead of spying?

For reference, this is my vitest test file:

import * as routerModule from '../../router.controller';

describe('test POST /endpoint', () => {
    it('successfully retrieves data from endpoint', async () => {
      const mockResponse = {
        status: 'success',
        data: {}
      };
      const functionSpy = vi.spyOn(routerModule, 'functionIWantToMock').mockResolvedValue(mockResponse);```
      
      
      const response = await fetch('http://localhost:5000/endpoint', {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
        },
        body: JSON.stringify({})
      })`