fix(stubs): Do not render function body in stub

[xanf]

@vue/test-utils v1 had special handing for functions in props when rendering stubs.

This PR makes @vue/test-utils v2 behave in the same way, even reusing same placeholder from https://github.com/vuejs/vue-test-utils/blob/97fdf18cd96f2ce19036d497ec98f2f76fc7b066/packages/create-instance/create-component-stubs.js#L21

(this allows us to run snaphot tests of vue2 and @vue/compat and to verify snapshots identity)

[netlify]

✅ Deploy Preview for vue-test-utils-docs ready!

Name	Link
🔨 Latest commit	0c68b20
🔍 Latest deploy log	https://app.netlify.com/sites/vue-test-utils-docs/deploys/634aa457db273c000a465df5
😎 Deploy Preview	https://deploy-preview-1819--vue-test-utils-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[freakzlike]

I think this will break using a function with .props().

const someFunction = wrapper.props('someFunction')
someFunction()

Maybe we can implement this logic into the wrapper.html() method?

[xanf]

I think this will break using a function with .props().

@freakzlike I don't think so

Code for copy-paste

  it('does not have problems on stubbing functions', () => {
    const ChildCmp = { template: '<div>child</div>', props: ['fn'] }
    const Root = {
      components: {
        ChildCmp
      },
      props: ['fn'],
      template: '<child-cmp :fn="fn">'
    }

    const fn = vi.fn()
    const wrapper = shallowMount(Root, { props: { fn } })
    expect(wrapper.findComponent(ChildCmp).props('fn')).toBe(fn)
    expect(wrapper.findComponent(ChildCmp).html()).toBe(
      '<child-cmp-stub fn="[Function]"></child-cmp-stub>'
    )
  })

When we're retrieving props - we are getting them on stub component. It get's replaced only for rendering child dom element

[freakzlike]

Well, then LGTM 👍