Fixes flaky spec by mocking debounce/throttle functions

* Removes all instances of mocked throttle from spec
* Removes all instances of mocked debounce from specs
* Adds global helper

ee/spec/frontend/analytics/cycle_analytics/components/custom_stage_form_spec.js

@@ -35,7 +35,6 @@ const MERGE_REQUEST_CLOSED = 'merge_request_closed';
 let store = null;
 const localVue = createLocalVue();
 localVue.use(Vuex);
-jest.mock('lodash/debounce', () => jest.fn);
 
 describe('CustomStageForm', () => {
   function createComponent(props = {}, stubs = {}) {

ee/spec/frontend/analytics/cycle_analytics/components/labels_selector_spec.js

@@ -20,8 +20,6 @@ const findFlashError = () => document.querySelector('.flash-container .flash-tex
 const mockGroupLabelsRequest = (status = 200) =>
   new MockAdapter(axios).onGet().reply(status, groupLabels);
 
-jest.mock('lodash/debounce', () => jest.fn);
-
 describe('Value Stream Analytics LabelsSelector', () => {
   let store = null;
   const localVue = createLocalVue();

ee/spec/frontend/analytics/cycle_analytics/components/tasks_by_type_filters_spec.js

@@ -32,7 +32,6 @@ const selectLabelAtIndex = (ctx, index) => {
 
 const mockGroupLabelsRequest = () => new MockAdapter(axios).onGet().reply(200, groupLabels);
 
-jest.mock('lodash/debounce', () => jest.fn);
 let store = null;
 const localVue = createLocalVue();
 localVue.use(Vuex);

ee/spec/frontend/approvals/components/mr_edit/rule_input_spec.js

@@ -4,8 +4,6 @@ import RuleInput from 'ee/approvals/components/mr_edit/rule_input.vue';
 import MREditModule from 'ee/approvals/stores/modules/mr_edit';
 import { createStoreOptions } from 'ee/approvals/stores';
 
-jest.mock('lodash/debounce', () => jest.fn(fn => fn));
-
 const localVue = createLocalVue();
 localVue.use(Vuex);
 

ee/spec/frontend/ide/stores/plugins/terminal_sync_spec.js

@@ -6,7 +6,6 @@ import { createStore } from '~/ide/stores';
 import eventHub from '~/ide/eventhub';
 
 jest.mock('ee/ide/lib/mirror');
-jest.mock('lodash/debounce', () => jest.fn);
 
 const ACTION_START = 'terminalSync/start';
 const ACTION_STOP = 'terminalSync/stop';

ee/spec/frontend/vue_shared/components/sidebar/epics_select/dropdown_search_input_spec.js

@@ -4,8 +4,6 @@ import { GlDeprecatedButton } from '@gitlab/ui';
 import DropdownSearchInput from 'ee/vue_shared/components/sidebar/epics_select/dropdown_search_input.vue';
 import Icon from '~/vue_shared/components/icon.vue';
 
-jest.mock('lodash/debounce', () => jest.fn(fn => fn));
-
 const createComponent = () =>
   shallowMount(DropdownSearchInput, {
     directives: {

spec/frontend/__mocks__/lodash/debounce.js

+// `lodash/debounce` has a non-trivial implementation which can lead to
+// [flaky spec errors][1]. This mock simply makes `debounce` calls synchronous.
+//
+// In the future we could enhance this by injecting some test values in
+// the function passed to it. See [this issue][2] for more information.
+//
+// [1]: https://gitlab.com/gitlab-org/gitlab/-/issues/212532
+// [2]: https://gitlab.com/gitlab-org/gitlab/-/issues/213378
+// Further reference: https://github.com/facebook/jest/issues/3465
+
+export default fn => fn;

spec/frontend/ide/components/branches/search_list_spec.js

@@ -9,8 +9,6 @@ import { branches } from '../../mock_data';
 const localVue = createLocalVue();
 localVue.use(Vuex);
 
-jest.mock('lodash/debounce', () => jest.fn);
-
 describe('IDE branches search list', () => {
   let wrapper;
   const fetchBranchesMock = jest.fn();

spec/frontend/ide/components/merge_requests/list_spec.js

@@ -134,9 +134,7 @@ describe('IDE merge requests list', () => {
         createComponent(defaultStateWithMergeRequests);
         const input = findTokenedInput();
         input.vm.$emit('input', 'something');
-        fetchMergeRequestsMock.mockClear();
 
-        jest.runAllTimers();
         return wrapper.vm.$nextTick().then(() => {
           expect(fetchMergeRequestsMock).toHaveBeenCalledWith(
             expect.any(Object),

spec/frontend/test_setup.js

@@ -20,7 +20,7 @@ afterEach(() =>
   // give Promises a bit more time so they fail the right test
   new Promise(setImmediate).then(() => {
     // wait for pending setTimeout()s
-    jest.runAllTimers();
+    jest.runOnlyPendingTimers();
   }),
 );