it('should observe iteration', () => {
    let dummy
    const list = reactive(['Hello'])
    const fn = jest.fn(() => (dummy = list.join(' ')));
    effect(fn)

    expect(fn).toHaveBeenCalledTimes(1) // normal

    expect(dummy).toBe('Hello')
    list.push('World!')
    expect(dummy).toBe('Hello World!')

    expect(fn).toHaveBeenCalledTimes(2) // normal

    list.shift()
    expect(dummy).toBe('World!')

    expect(fn).toHaveBeenCalledTimes(5) // It depends on list.length
  })