如何在wrapper.vm中使用jest.spyOn？Vue3组合式API测试报错

测试时调整时序，先创建spy再触发事件：
```javascript
it('calls buildList when child emits mounted', async () => {
  const wrapper = mount(YourParentComponent);
  // 先创建spy
  const buildListSpy = jest.spyOn(wrapper.vm, 'buildList');
  
  // 再触发事件
  await wrapper.findComponent(ClientTableExpandable).vm.$emit('mounted');
  
  expect(buildListSpy).toHaveBeenCalled();
});

内容的提问来源于stack exchange，提问作者Gabriella Tavares