vuejs/vitest: How to test/mock composition functions

I’m kinda stuck with testing composition-functions. I’m using vitest with @vue/test-utils, but also found no good way to get it to work with jest.

My issue is: How do I test composable functions, which use other composable functions? And how do I correctly mock the functions return values?

Let’s say I have a composition like this:

import {useExternalComposition} from '@/composables/externalComposition'

export function useFoo() {
  function isConditionTrue(condition) {
    if (condition) {
      return false;
    }
    return true;
  }
  
  async function bar() {
    const { externalFunction1, externalFunction2} = useExternalComposition();
    const isTrue = isConditionTrue(true);
    try {
      if (isTrue) {
        await externalFunction1();
        return;
      } 
      await externalFunction2();
    } catch(e) {
      console.error(e);
    }
  }
  
  return {
    bar, 
    isConditionTrue
  }
}

With vitest I was not able to figure out a way, to correctly test bar, in detail to mock results from isConditionTrue and externalFunction1 and externalFunction2.

This was my best approach for now:

it('should call isConditionTrue', async function () {
  const useFooVar = useFoo();
  const spy = vi
    .spyOn(useFooVar, 'isConditionTrue')
    .mockImplementationOnce(() => true);

  expect(spy.getMockName()).toEqual('isConditionTrue'); // true

  await useFooVar.bar();
  expect(spy).toHaveBeenCalled(); // AssertionError: expected "isConditionTrue" to be called at least once
});

What do I miss?

I tried multiple ways of mocking/spying functions, and expected to have a correct assertion