Migrate mr_widget_author_time to VTU

spec/frontend/vue_mr_widget/components/mr_widget_author_time_spec.js

-import Vue from 'vue';
-import mountComponent from 'helpers/vue_mount_component_helper';
+import { shallowMount } from '@vue/test-utils';
+import MrWidgetAuthor from '~/vue_merge_request_widget/components/mr_widget_author.vue';
 import MrWidgetAuthorTime from '~/vue_merge_request_widget/components/mr_widget_author_time.vue';
 
 describe('MrWidgetAuthorTime', () => {
-  let vm;
+  let wrapper;
+
+  const defaultProps = {
+    actionText: 'Merged by',
+    author: {
+      name: 'Administrator',
+      username: 'root',
+      webUrl: 'http://localhost:3000/root',
+      avatarUrl: 'http://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon',
+    },
+    dateTitle: '2017-03-23T23:02:00.807Z',
+    dateReadable: '12 hours ago',
+  };
 
   beforeEach(() => {
-    const Component = Vue.extend(MrWidgetAuthorTime);
-
-    vm = mountComponent(Component, {
-      actionText: 'Merged by',
-      author: {
-        name: 'Administrator',
-        username: 'root',
-        webUrl: 'http://localhost:3000/root',
-        avatarUrl:
-          'http://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon',
-      },
-      dateTitle: '2017-03-23T23:02:00.807Z',
-      dateReadable: '12 hours ago',
+    wrapper = shallowMount(MrWidgetAuthorTime, {
+      propsData: defaultProps,
     });
   });
 
   afterEach(() => {
-    vm.$destroy();
+    wrapper.destroy();
   });
 
   it('renders provided action text', () => {
-    expect(vm.$el.textContent).toContain('Merged by');
+    expect(wrapper.text()).toContain('Merged by');
   });
 
   it('renders author', () => {
-    expect(vm.$el.textContent).toContain('Administrator');
+    expect(wrapper.find(MrWidgetAuthor).props('author')).toStrictEqual(defaultProps.author);
   });
 
   it('renders provided time', () => {
-    expect(vm.$el.querySelector('time').getAttribute('title')).toEqual('2017-03-23T23:02:00.807Z');
+    expect(wrapper.find('time').attributes('title')).toBe('2017-03-23T23:02:00.807Z');
 
-    expect(vm.$el.querySelector('time').textContent.trim()).toEqual('12 hours ago');
+    expect(wrapper.find('time').text().trim()).toBe('12 hours ago');
   });
 });