[Bug]: Vitest plugin not using Vue slots defined in args

[tfoxkiu]

Describe the bug

When using Vitest plugin in a Vue Storybook, the stories rendered in Vitest doesn't have the passed slots.

Story:

Vitest:

To Reproduce

TestButton.vue

<script setup></script>

<template>
  <button>Slot: <slot /></button>
</template>

TestButton.stories.js

import { h } from 'vue'
import TestButton from './TestButton.vue'
import { expect } from '@storybook/test'

export default {
  component: TestButton
}

export const TextSlot = {
  args: {
    default: 'Primary'
  },
  play: async ({ args, canvasElement }) => {
    await expect(canvasElement.textContent).toContain(args.default)
  }
}

export const FunctionSlot = {
  args: {
    default: () => h('span', 'Primary')
  },
  play: async ({ canvasElement }) => {
    await expect(canvasElement.textContent).toContain('Primary')
  }
}

Configuration of Storybook is the standard one.

Full repro repo: https://github.com/tfoxkiu/storybook-vitest-vue-slots

System

Storybook Environment Info:

  System:
    OS: Linux 6.8 Ubuntu 24.04.1 LTS 24.04.1 LTS (Noble Numbat)
    CPU: (12) x64 AMD Ryzen 5 5500
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 20.16.0 - ~/.local/share/mise/installs/node/20.16.0/bin/node
    npm: 10.8.1 - ~/.local/share/mise/installs/node/20.16.0/bin/npm <----- active
  Browsers:
    Chrome: 131.0.6778.69
  npmPackages:
    @storybook/addon-essentials: ^8.4.5 => 8.4.5 
    @storybook/experimental-addon-test: ^8.4.5 => 8.4.5 
    @storybook/test: ^8.4.5 => 8.4.5 
    @storybook/vue3: ^8.4.5 => 8.4.5 
    @storybook/vue3-vite: ^8.4.5 => 8.4.5 
    eslint-plugin-storybook: ^0.8.0 => 0.8.0 
    msw-storybook-addon: ^2.0.4 => 2.0.4 
    storybook: ^8.4.5 => 8.4.5

Additional context

No response