Extract a re-used event name to the constants file

This extended description is here to please
Danger, which doesn't account for
succinct-but-complete message subjects.

app/assets/javascripts/diffs/components/collapsed_files_warning.vue

 <script>
 import { GlAlert, GlButton } from '@gitlab/ui';
 
-import { CENTERED_LIMITED_CONTAINER_CLASSES } from '../constants';
+import { CENTERED_LIMITED_CONTAINER_CLASSES, EVT_EXPAND_ALL_FILES } from '../constants';
 import eventHub from '../event_hub';
 
 export default {
@@ -40,7 +40,7 @@ export default {
       this.$emit('dismiss');
     },
     expand() {
-      eventHub.$emit('mr:diffs:expandAllFiles');
+      eventHub.$emit(EVT_EXPAND_ALL_FILES);
       this.dismiss();
     },
   },

app/assets/javascripts/diffs/components/compare_versions.vue

@@ -6,7 +6,7 @@ import { polyfillSticky } from '~/lib/utils/sticky';
 import CompareDropdownLayout from './compare_dropdown_layout.vue';
 import SettingsDropdown from './settings_dropdown.vue';
 import DiffStats from './diff_stats.vue';
-import { CENTERED_LIMITED_CONTAINER_CLASSES } from '../constants';
+import { CENTERED_LIMITED_CONTAINER_CLASSES, EVT_EXPAND_ALL_FILES } from '../constants';
 import eventHub from '../event_hub';
 
 export default {
@@ -71,7 +71,7 @@ export default {
       'toggleShowTreeList',
     ]),
     expandAllFiles() {
-      eventHub.$emit('mr:diffs:expandAllFiles');
+      eventHub.$emit(EVT_EXPAND_ALL_FILES);
     },
   },
 };

app/assets/javascripts/diffs/components/diff_file.vue

@@ -11,7 +11,11 @@ import DiffFileHeader from './diff_file_header.vue';
 import DiffContent from './diff_content.vue';
 import { diffViewerErrors } from '~/ide/constants';
 import { collapsedType, isCollapsed } from '../diff_file';
-import { DIFF_FILE_AUTOMATIC_COLLAPSE, DIFF_FILE_MANUAL_COLLAPSE } from '../constants';
+import {
+  DIFF_FILE_AUTOMATIC_COLLAPSE,
+  DIFF_FILE_MANUAL_COLLAPSE,
+  EVT_EXPAND_ALL_FILES,
+} from '../constants';
 import { DIFF_FILE, GENERIC_ERROR } from '../i18n';
 import eventHub from '../event_hub';
 
@@ -154,10 +158,10 @@ export default {
   },
   created() {
     notesEventHub.$on(`loadCollapsedDiff/${this.file.file_hash}`, this.requestDiff);
-    eventHub.$on('mr:diffs:expandAllFiles', this.expandAllListener);
+    eventHub.$on(EVT_EXPAND_ALL_FILES, this.expandAllListener);
   },
   beforeDestroy() {
-    eventHub.$off('mr:diffs:expandAllFiles', this.expandAllListener);
+    eventHub.$off(EVT_EXPAND_ALL_FILES, this.expandAllListener);
   },
   methods: {
     ...mapActions('diffs', [

app/assets/javascripts/diffs/constants.js

@@ -95,3 +95,6 @@ export const RENAMED_DIFF_TRANSITIONS = {
   [`${STATE_ERRORED}:${TRANSITION_LOAD_START}`]: STATE_LOADING,
   [`${STATE_ERRORED}:${TRANSITION_ACKNOWLEDGE_ERROR}`]: STATE_IDLING,
 };
+
+// MR Diffs known events
+export const EVT_EXPAND_ALL_FILES = 'mr:diffs:expandAllFiles';

spec/frontend/diffs/components/collapsed_files_warning_spec.js

@@ -2,7 +2,7 @@ import Vuex from 'vuex';
 import { shallowMount, mount, createLocalVue } from '@vue/test-utils';
 import createStore from '~/diffs/store/modules';
 import CollapsedFilesWarning from '~/diffs/components/collapsed_files_warning.vue';
-import { CENTERED_LIMITED_CONTAINER_CLASSES } from '~/diffs/constants';
+import { CENTERED_LIMITED_CONTAINER_CLASSES, EVT_EXPAND_ALL_FILES } from '~/diffs/constants';
 import eventHub from '~/diffs/event_hub';
 
 const propsData = {
@@ -77,13 +77,13 @@ describe('CollapsedFilesWarning', () => {
     expect(wrapper.find('[data-testid="root"]').exists()).toBe(false);
   });
 
-  it('emits the `mr:diffs:expandAllFiles` event when the alert action button is clicked', () => {
+  it(`emits the \`${EVT_EXPAND_ALL_FILES}\` event when the alert action button is clicked`, () => {
     createComponent({}, { full: true });
 
     jest.spyOn(eventHub, '$emit');
 
     getAlertActionButton().vm.$emit('click');
 
-    expect(eventHub.$emit).toHaveBeenCalledWith('mr:diffs:expandAllFiles');
+    expect(eventHub.$emit).toHaveBeenCalledWith(EVT_EXPAND_ALL_FILES);
   });
 });

spec/frontend/diffs/components/diff_file_spec.js

@@ -12,6 +12,7 @@ import DiffContentComponent from '~/diffs/components/diff_content.vue';
 import eventHub from '~/diffs/event_hub';
 
 import { diffViewerModes, diffViewerErrors } from '~/ide/constants';
+import { EVT_EXPAND_ALL_FILES } from '~/diffs/constants';
 
 function changeViewer(store, index, { automaticallyCollapsed, manuallyCollapsed, name }) {
   const file = store.state.diffs.diffFiles[index];
@@ -140,7 +141,7 @@ describe('DiffFile', () => {
   });
 
   describe('collapsing', () => {
-    describe('`mr:diffs:expandAllFiles` event', () => {
+    describe(`\`${EVT_EXPAND_ALL_FILES}\` event`, () => {
       beforeEach(() => {
         jest.spyOn(wrapper.vm, 'handleToggle').mockImplementation(() => {});
       });
@@ -150,13 +151,13 @@ describe('DiffFile', () => {
 
         await wrapper.vm.$nextTick();
 
-        eventHub.$emit('mr:diffs:expandAllFiles');
+        eventHub.$emit(EVT_EXPAND_ALL_FILES);
 
         expect(wrapper.vm.handleToggle).toHaveBeenCalledTimes(1);
       });
 
       it('does nothing when the file is not collapsed', async () => {
-        eventHub.$emit('mr:diffs:expandAllFiles');
+        eventHub.$emit(EVT_EXPAND_ALL_FILES);
 
         await wrapper.vm.$nextTick();