fix(runtim-utils): do not use defu for merging

examples/app-vitest-full/tests/nuxt/mount-suspended.spec.ts

@@ -249,6 +249,30 @@ describe.each(Object.entries(formats))(`%s`, (name, component) => {
     expect(wrapper.html()).toEqual(`
 <div>
   <h1>${name}</h1><pre>updated title</pre><pre>XHello nuxt-vitest</pre><span>hello</span><span>nuxt</span><span>vitest</span><span>myObjProp: {}</span>
+</div>
+    `.trim())
+  })
+
+  it('can be updated to null with setProps', async () => {
+    await wrapper.setProps({
+      myProp: 'updated title',
+      myObjProp: null,
+    })
+    expect(wrapper.html()).toEqual(`
+<div>
+  <h1>${name}</h1><pre>updated title</pre><pre>XHello nuxt-vitest</pre><span>hello</span><span>nuxt</span><span>vitest</span><span>myObjProp: null</span>
+</div>
+    `.trim())
+  })
+
+  it('can be updated to undefined with setProps', async () => {
+    await wrapper.setProps({
+      myProp: 'updated title',
+      myObjProp: undefined,
+    })
+    expect(wrapper.html()).toEqual(`
+<div>
+  <h1>${name}</h1><pre>updated title</pre><pre>XHello nuxt-vitest</pre><span>hello</span><span>nuxt</span><span>vitest</span><span>myObjProp: {}</span>
 </div>
     `.trim())
   })

src/runtime-utils/mount.ts

@@ -2,7 +2,7 @@ import { mount } from '@vue/test-utils'
 import type { ComponentMountingOptions } from '@vue/test-utils'
 import { Suspense, h, isReadonly, nextTick, reactive, unref, getCurrentInstance } from 'vue'
 import type { DefineComponent, SetupContext } from 'vue'
-import { defu, createDefu } from 'defu'
+import { defu } from 'defu'
 import type { RouteLocationRaw } from 'vue-router'
 
 import { RouterLink } from './components/RouterLink'
@@ -166,7 +166,7 @@ export async function mountSuspended<T>(
                         setup: setup ? (props: Record<string, unknown>) => wrappedSetup(props, setupContext) : undefined,
                       }
 
-                      return () => h(clonedComponent, { ...customMerge(setProps, props) as typeof props, ...attrs }, slots)
+                      return () => h(clonedComponent, { ...props, ...setProps, ...attrs }, slots)
                     },
                   }),
               },
@@ -201,11 +201,6 @@ interface AugmentedVueInstance {
   __setProps?: (props: Record<string, unknown>) => void
 }
 
-const customMerge = createDefu((obj, key, value) => {
-  obj[key] = value
-  return true
-})
-
 function cloneProps(props: Record<string, unknown>) {
   const newProps = reactive<Record<string, unknown>>({})
   for (const key in props) {