test: refactor many test suites to use testUtils/initializeMocks (#2067)

Simplifies a bunch of test code by converting it to use our handy testUtils module.

None of the app code is change, just test code. And none of the test cases are modified in any meaningful way - this just simplifies the setup/cleanup significantly.

src/course-checklist/ChecklistSection/ChecklistSection.test.jsx

@@ -4,9 +4,7 @@ import {
   initializeMocks, render, screen, within,
 } from '../../testUtils';
 import { getApiWaffleFlagsUrl } from '../../data/api';
-import { fetchWaffleFlags } from '../../data/thunks';
 import { generateCourseLaunchData } from '../factories/mockApiResponses';
-import { executeThunk } from '../../utils';
 import { checklistItems } from './utils/courseChecklistData';
 import messages from './messages';
 
@@ -34,7 +32,7 @@ const renderComponent = (props) => {
 
 describe('ChecklistSection', () => {
   beforeEach(async () => {
-    const { axiosMock, reduxStore } = initializeMocks();
+    const { axiosMock } = initializeMocks();
     axiosMock
       .onGet(getApiWaffleFlagsUrl(courseId))
       .reply(200, {
@@ -43,7 +41,6 @@ describe('ChecklistSection', () => {
         useNewScheduleDetailsPage: true,
         useNewCourseOutlinePage: true,
       });
-    await executeThunk(fetchWaffleFlags(courseId), reduxStore.dispatch);
   });
 
   it('a heading using the dataHeading prop', () => {