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Sorry for my late response. I have tried a few things and now its says: "React is not defined"

Here is my component: 
> `<script setup>
> import { useAuthStore } from '@/store'
> </script>
> 
> <template>
>   <el-form>
>     <el-form-item label="Username">
>       <el-input />
>     </el-form-item>
>     <el-form-item label="Password">
>       <el-input placeholder="Please input password" show-password />
>     </el-form-item>
>     <el-form-item>
>       <el-button type="primary" @click="">Login</el-button>
>     </el-form-item>
>   </el-form>
> </template>`

import { mount } from '@cypress/vue'
import Login from './Login.vue'

describe('<Login />', () => {
  it('renders', () => {
    cy.viewport(1280, 720)
    mount(<Login />)
  })
})

this is working:
`import { mount } from '@cypress/vue'
import Login from './Login.vue'

describe('<Login />', () => {
  it('renders', () => {
    cy.viewport(1280, 720)
    mount(Login)
  })
})`

Do you use vite ? Is your file with extension `.jsx` ?

I think the problem is vue 2 with composition API. In my vue 3 projects is it working fine.