I have just started writing unit tests. I understand that testing private functions is bad practice (with exceptions i guess).
However, i have not found any clear information on the following:

If I test a publicly available function that calls a private one directly, is it okay to mock the private one and ‘call’ it from within the test?

So this is the code i want to test:

async asserUser(
    user: CurrentUser,
    id: string,
  ): Promise<void> {
    if (!(await this.userHasAccess(user.id, id))) {
      throw new ForbiddenException(
        'some error message',
      );
    }
  }

I have written this test:

  it('should throw an exception', async () => {
      const userHasAccessMock = jest.spyOn(
        service.prototype as any,
        'userHasAccess',
      );
      userHasAccess.mockReturnValue(false);

      expect(() => service.asserUser(mockUser, mockId)).toThrow(
        ForbiddenException,
      );
    });

Is mocking userHasAccess okay in this context? If yes, have i done it the correct way? If no, how would i proceed in testing this whole thing?

Thanks.