fix: remove wrapper div when unmount (#2700)

Fixes #2690

Author: CaptainWang98

src/mount.ts

@@ -99,6 +99,9 @@ export function mount(
     }
 
     to.appendChild(el)
+    app.onUnmount(() => {
+      to?.removeChild(el)
+    })
   }
   const vm = app.mount(el)
   if (errorsOnMount.length) {

tests/mount.spec.ts

@@ -102,4 +102,20 @@ describe('mount: general tests', () => {
     })
     expect(wrapper.text()).toContain('Hello world')
   })
+
+  it('should remove wrapper div when unmount', () => {
+    expect(document.body.firstChild, 'Container should be empty').toBeNull()
+
+    const wrapper = mount(Hello, {
+      props: { msg: 'Hello world' },
+      attachTo: document.body
+    })
+    expect(
+      document.body.firstChild,
+      'Container should have mounted component wrapper'
+    ).toBeInstanceOf(HTMLDivElement)
+
+    wrapper.unmount()
+    expect(document.body.firstChild, 'Container should be empty').toBeNull()
+  })
 })