Mock working in test file but not in tested file

I’m trying to migrate a project from Jest to Vitest and I’m having issues with mocks. I can’t figure out why, when mocking a third party module and using mock implementations/mock returned values, these do work inside the test file, but not inside the tested file (where I want the mocked values to actually return). This works without issues with Jest but not with Vitest. Here’s some of the code I have currently:

import internalService from '@internal/js-service'
import idUtil from '@internal/js-service/lib/idUtil'

vi.mock('@internal/js-service', () => {
    return {
      default: {
        init: vi.fn().mockReturnValue('1),
        identify: vi.fn(),
      },
    }
  })

vi.mock('@internal/js-service/lib/idUtil', () => ({
    default: vi.fn().mockReturnValue('123'),
  }))

test('should initialize the internal service with the expected params',  () => {
    console.log('test', internalService.init(), idUtil())

    initializeInternalService({email: '[email protected]'})

    expect(internalService.init).toHaveBeenCalledTimes(1)
    expect(internalService.init).toHaveBeenCalledWith(
      {
        email: '[email protected]',
        unique_id: '1',
      },
    )
  })

and the tested file:

import internalService from '@internal/js-service'
import idUtil from '@internal/js-service/lib/idUtil'

export const initializeInternalService = (user: User) => {
  internalService.init(
    {
      unique_id: idUtil(),
      email: user.email,
    },
  )
}

When the console.log runs inside the test, the code returns the mocked values ('1' and '123') as expected, but when running the code in the tested file it seems like the original implementations are run, not the mocked ones, and I don’t understand why.