Bug: Emit doesn't update 2 way bound props

src/emit.ts

@@ -48,7 +48,7 @@ function recordEvent(
   events: Events,
   vm: ComponentInternalInstance,
   event: string,
-  args: Events[number]
+  args: unknown[]
 ): void {
   // Functional component wrapper creates a parent component
   let wrapperVm = vm
@@ -64,4 +64,16 @@ function recordEvent(
 
   // Record the event message sent by the emit
   events[cid][event].push(args)
+
+  if (event.startsWith('update:')) {
+    if (args.length !== 1) {
+      throw new Error(
+        'Two-way bound properties have to emit a single value. ' +
+          args.length +
+          ' values given.'
+      )
+    }
+
+    vm.props[event.slice('update:'.length)] = args[0]
+  }
 }

tests/props.spec.ts

@@ -1,6 +1,7 @@
 import { mount } from '../src'
 import WithProps from './components/WithProps.vue'
 import Hello from './components/Hello.vue'
+import { defineComponent } from 'vue'
 
 describe('props', () => {
   it('returns a single prop applied to a component', () => {
@@ -82,4 +83,32 @@ describe('props', () => {
       object: {}
     })
   })
+
+  it('should return the updated props on 2 way binding', async () => {
+    const component = defineComponent({
+      template: '<button @click="increment"></button>',
+      props: {
+        modelValue: {
+          type: Number,
+          required: true
+        }
+      },
+      emits: ['update:modelValue'],
+      setup(props, ctx) {
+        return {
+          increment: () => ctx.emit('update:modelValue', props.modelValue + 1)
+        }
+      }
+    })
+
+    const wrapper = mount(component, {
+      props: {
+        modelValue: 1
+      }
+    })
+
+    expect(wrapper.props('modelValue')).toBe(1)
+    await wrapper.trigger('click')
+    expect(wrapper.props('modelValue')).toBe(2)
+  })
 })