How to spy the store's $reset method in tests with vitest

[meiyerDev]

Suppose we have the following code:

Store declaration

// src/stores/main.ts

export const useMainStore = defineStore('main', {
  state: () => ({ isLoading: false })
});

Use of the store

// src/actions/reset.ts

export const resetApp = () => {
  const mainStore = useMainStore();
  mainStore.$reset();
};

Test declaration

describe('MainStore', () => {
    beforeEach(() => {
        setActivePinia(createTestingPinia());
    });

   it('resetApp must be reset store', () => {
      const mainStore = useMainStore();

      resetApp();

     // THIS IS SUCCESSFUL
     expect(mainStore.$patch).toHaveBeenCalled();

     // THIS IS FAILED
     expect(mainStore.$reset).toHaveBeenCalled();
   });
});

Why the store's $reset method fails in the assertion but the $patch method is successful?

I understand that the $reset method may be using the $patch method to reset the store, but it isn't spied. If we try to use this code

expect(mainStore.$reset).toHaveBeenCalled();

This fails with exception: TypeError: [Function $reset] is not a spy or a call to a spy!