test: improve coverage

Author: yyx990803

Diff for: src/core/instance/render.js

@@ -49,6 +49,7 @@ export function initRender (vm: Component) {
   // $attrs & $listeners are exposed for easier HOC creation.
   // they need to be reactive so that HOCs using them are always updated
   const parentData = parentVnode && parentVnode.data
+  /* istanbul ignore else */
   if (process.env.NODE_ENV !== 'production') {
     defineReactive(vm, '$attrs', parentData && parentData.attrs, () => {
       !isUpdatingChildComponent && warn(`$attrs is readonly.`, vm)

Diff for: src/platforms/web/runtime/components/transition-group.js

@@ -127,6 +127,7 @@ export default {
       if (!hasTransition) {
         return false
       }
+      /* istanbul ignore if */
       if (this._hasMove) {
         return this._hasMove
       }

Diff for: test/unit/features/directives/on.spec.js

@@ -695,4 +695,18 @@ describe('Directive v-on', () => {
     expect(mouseup.calls.count()).toBe(1)
     expect(mousedown.calls.count()).toBe(1)
   })
+
+  it('warn object syntax with modifier', () => {
+    new Vue({
+      template: `<button v-on.self="{}"></button>`
+    }).$mount()
+    expect(`v-on without argument does not support modifiers`).toHaveBeenWarned()
+  })
+
+  it('warn object syntax with non-object value', () => {
+    new Vue({
+      template: `<button v-on="123"></button>`
+    }).$mount()
+    expect(`v-on without argument expects an Object value`).toHaveBeenWarned()
+  })
 })