fix: expose with render function

Fixes #1065

When we are testing a component with a render function returned by the setup,
then its proxy will be empty.
The behavior difference can be seen in vue-next [here](https://github.com/vuejs/vue-next/blob/d19cfc0503dddbded5e599bef0965aba3d25ca28/packages/runtime-core/src/component.ts#L674).
In that case, `wrapper.vm` will be empty if we return `vm.$.proxy`.
To handle it, we return `vm` directly for such components,
allowing at least what is exposed publicly to be available on `wrapper.vm`.

src/vueWrapper.ts

@@ -36,12 +36,20 @@ export class VueWrapper<T extends ComponentPublicInstance>
     this.__app = app
     // root is null on functional components
     this.rootVM = vm?.$root
-    // vm.$.proxy is what the template has access to
+    // `vm.$.proxy` is what the template has access to
     // so even if the component is closed (as they are by default for `script setup`)
     // a test will still be able to do something like
     // `expect(wrapper.vm.count).toBe(1)`
-    // (note that vm can be null for functional components, hence the condition)
-    this.componentVM = vm ? (vm.$.proxy as T) : (vm as T)
+    // if we return it as `vm`
+    // This does not work for functional components though (as they have no vm)
+    // or for components with a setup that returns a render function (as they have an empty proxy)
+    // in both cases, we return `vm` directly instead
+    this.componentVM =
+      vm &&
+      // a component with a setup that returns a render function will have no `devtoolsRawSetupState`
+      (vm.$ as unknown as { devtoolsRawSetupState: any }).devtoolsRawSetupState
+        ? ((vm.$ as any).proxy as T)
+        : (vm as T)
     this.__setProps = setProps
 
     this.attachNativeEventListener()

tests/components/DefineExposeWithRenderFunction.vue

@@ -0,0 +1,14 @@
+<script lang="ts">
+import { defineComponent, h, ref } from 'vue'
+
+export default defineComponent({
+  name: 'Hello',
+
+  setup(props, { expose }) {
+    const other = ref('other')
+    const msg = ref('Hello world');
+    expose({ other })
+    return () => [h('div', msg.value), h('div', other.value)]
+  }
+})
+</script>

tests/expose.spec.ts

@@ -1,6 +1,7 @@
 import { mount } from '../src'
 import Hello from './components/Hello.vue'
 import DefineExpose from './components/DefineExpose.vue'
+import DefineExposeWithRenderFunction from './components/DefineExposeWithRenderFunction.vue'
 import ScriptSetupExpose from './components/ScriptSetup_Expose.vue'
 import ScriptSetup from './components/ScriptSetup.vue'
 
@@ -20,6 +21,16 @@ describe('expose', () => {
     expect(wrapper.vm.msg).toBe('Hello world')
   })
 
+  it('access vm on simple components with custom `expose` and a setup returning a render function', async () => {
+    const wrapper = mount(DefineExposeWithRenderFunction)
+
+    // other is exposed vie `expose`
+    expect(wrapper.vm.other).toBe('other')
+    // can't access `msg` as it is not exposed
+    // and we are in a component with a setup returning a render function
+    expect(wrapper.vm.msg).toBeUndefined()
+  })
+
   it('access vm with <script setup> and defineExpose()', async () => {
     const wrapper = mount(ScriptSetupExpose)