fix(VRadioGroup): emit the new value when reset

fixes #4752

Author: KaelWD

src/components/VInput/VInput.js

@@ -93,7 +93,7 @@ export default {
       },
       set (val) {
         this.lazyValue = val
-        this.$emit('input', val)
+        this.$emit(this.$_modelEvent, val)
       }
     },
     isDirty () {
@@ -113,6 +113,12 @@ export default {
     }
   },
 
+  beforeCreate () {
+    // v-radio-group needs to emit a different event
+    // https://github.com/vuetifyjs/vuetify/issues/4752
+    this.$_modelEvent = (this.$options.model && this.$options.model.event) || 'input'
+  },
+
   methods: {
     genContent () {
       return [

src/mixins/selectable.js

@@ -80,7 +80,7 @@ export default {
 
   watch: {
     inputValue (val) {
-      this.internalValue = val
+      this.lazyValue = val
     }
   },
 

test/unit/components/VRadioGroup/VRadioGroup.spec.js

@@ -332,4 +332,23 @@ test('VRadioGroup.vue', ({ mount }) => {
     radio.first('input').trigger('change')
     expect(onChange).not.toBeCalled()
   })
+
+  it('should reset', async () => {
+    const wrapper = mount(VRadioGroup, {
+      propsData: {
+        value: '0'
+      },
+      slots: {
+        default: [VRadio]
+      }
+    })
+    const change = jest.fn()
+    wrapper.vm.$on('change', change)
+
+    wrapper.vm.reset()
+    await wrapper.vm.$nextTick()
+
+    expect(change).toHaveBeenCalledTimes(1)
+    expect(change).toHaveBeenCalledWith(undefined)
+  })
 })