improve $props test case

test/unit/features/instance/properties.spec.js

@@ -80,20 +80,49 @@ describe('Instance properties', () => {
     expect(calls).toEqual(['outer:undefined', 'middle:outer', 'inner:middle', 'next:undefined'])
   })
 
-  it('$props', () => {
-    var Comp = Vue.extend({
+  it('$props', done => {
+    const Comp = Vue.extend({
       props: ['msg'],
-      template: '<div>{{ msg }}</div>'
+      template: '<div>{{ msg }} {{ $props.msg }}</div>'
     })
-    var vm = new Comp({
+    const vm = new Comp({
       propsData: {
         msg: 'foo'
       }
-    })
+    }).$mount()
+    // check render
+    expect(vm.$el.textContent).toContain('foo foo')
+    // warn set
+    vm.$props = {}
+    expect('$props is readonly').toHaveBeenWarned()
     // check existence
     expect(vm.$props.msg).toBe('foo')
     // check change
-    Vue.set(vm, 'msg', 'bar')
+    vm.msg = 'bar'
     expect(vm.$props.msg).toBe('bar')
+    waitForUpdate(() => {
+      expect(vm.$el.textContent).toContain('bar bar')
+    }).then(() => {
+      vm.$props.msg = 'baz'
+      expect(vm.msg).toBe('baz')
+    }).then(() => {
+      expect(vm.$el.textContent).toContain('baz baz')
+    }).then(done)
+  })
+
+  it('warn mutating $props', () => {
+    const Comp = {
+      props: ['msg'],
+      render () {},
+      mounted () {
+        expect(this.$props.msg).toBe('foo')
+        this.$props.msg = 'bar'
+      }
+    }
+    new Vue({
+      template: `<comp ref="comp" msg="foo" />`,
+      components: { Comp }
+    }).$mount()
+    expect(`Avoid mutating a prop`).toHaveBeenWarned()
   })
 })