Migrate mr_widget_related_links to VTU

spec/frontend/vue_mr_widget/components/mr_widget_related_links_spec.js

-import Vue from 'vue';
-import mountComponent from 'helpers/vue_mount_component_helper';
-import relatedLinksComponent from '~/vue_merge_request_widget/components/mr_widget_related_links.vue';
+import { shallowMount } from '@vue/test-utils';
+import RelatedLinks from '~/vue_merge_request_widget/components/mr_widget_related_links.vue';
 
 describe('MRWidgetRelatedLinks', () => {
-  let vm;
+  let wrapper;
 
-  const createComponent = (data) => {
-    const Component = Vue.extend(relatedLinksComponent);
-
-    return mountComponent(Component, data);
+  const createComponent = (propsData = {}) => {
+    wrapper = shallowMount(RelatedLinks, { propsData });
   };
 
   afterEach(() => {
-    vm.$destroy();
+    wrapper.destroy();
   });
 
   describe('computed', () => {
     describe('closesText', () => {
       it('returns Closes text for open merge request', () => {
-        vm = createComponent({ state: 'open', relatedLinks: {} });
+        createComponent({ state: 'open', relatedLinks: {} });
 
-        expect(vm.closesText).toEqual('Closes');
+        expect(wrapper.vm.closesText).toBe('Closes');
       });
 
       it('returns correct text for closed merge request', () => {
-        vm = createComponent({ state: 'closed', relatedLinks: {} });
+        createComponent({ state: 'closed', relatedLinks: {} });
 
-        expect(vm.closesText).toEqual('Did not close');
+        expect(wrapper.vm.closesText).toBe('Did not close');
       });
 
       it('returns correct tense for merged request', () => {
-        vm = createComponent({ state: 'merged', relatedLinks: {} });
+        createComponent({ state: 'merged', relatedLinks: {} });
 
-        expect(vm.closesText).toEqual('Closed');
+        expect(wrapper.vm.closesText).toBe('Closed');
       });
     });
   });
 
   it('should have only have closing issues text', () => {
-    vm = createComponent({
+    createComponent({
       relatedLinks: {
         closing: '<a href="#">#23</a> and <a>#42</a>',
       },
     });
-    const content = vm.$el.textContent.replace(/\n(\s)+/g, ' ').trim();
+    const content = wrapper
+      .text()
+      .replace(/\n(\s)+/g, ' ')
+      .trim();
 
     expect(content).toContain('Closes #23 and #42');
     expect(content).not.toContain('Mentions');
   });
 
   it('should have only have mentioned issues text', () => {
-    vm = createComponent({
+    createComponent({
       relatedLinks: {
         mentioned: '<a href="#">#7</a>',
       },
     });
 
-    expect(vm.$el.innerText).toContain('Mentions #7');
-    expect(vm.$el.innerText).not.toContain('Closes');
+    expect(wrapper.text().trim()).toContain('Mentions #7');
+    expect(wrapper.text().trim()).not.toContain('Closes');
   });
 
   it('should have closing and mentioned issues at the same time', () => {
-    vm = createComponent({
+    createComponent({
       relatedLinks: {
         closing: '<a href="#">#7</a>',
         mentioned: '<a href="#">#23</a> and <a>#42</a>',
       },
     });
-    const content = vm.$el.textContent.replace(/\n(\s)+/g, ' ').trim();
+    const content = wrapper
+      .text()
+      .replace(/\n(\s)+/g, ' ')
+      .trim();
 
     expect(content).toContain('Closes #7');
     expect(content).toContain('Mentions #23 and #42');
   });
 
   it('should have assing issues link', () => {
-    vm = createComponent({
+    createComponent({
       relatedLinks: {
         assignToMe: '<a href="#">Assign yourself to these issues</a>',
       },
     });
 
-    expect(vm.$el.innerText).toContain('Assign yourself to these issues');
+    expect(wrapper.text().trim()).toContain('Assign yourself to these issues');
   });
 });