Added scroll_helper tests

app/assets/javascripts/dispatcher.js

@@ -54,7 +54,7 @@ import RefSelectDropdown from './ref_select_dropdown';
 import GfmAutoComplete from './gfm_auto_complete';
 import ShortcutsBlob from './shortcuts_blob';
 import initSettingsPanels from './settings_panels';
-import { setScrollWidth } from './helpers/scroll_helper';
+import ScrollHelper from './helpers/scroll_helper';
 
 (function() {
   var Dispatcher;
@@ -77,7 +77,7 @@ import { setScrollWidth } from './helpers/scroll_helper';
         return false;
       }
 
-      setScrollWidth();
+      ScrollHelper.setScrollWidth();
 
       path = page.split(':');
       shortcut_handler = null;

app/assets/javascripts/helpers/scroll_helper.js

-function getScrollWidth() {
+import $ from 'jquery';
+
+const ScrollHelper = {
+  getScrollWidth() {
     const $rulerContainer = $('<div>').css({
       visibility: 'hidden',
       width: 100,
@@ -17,13 +20,11 @@ function getScrollWidth() {
     $rulerContainer.remove();
 
     return 100 - scrollWidth;
-}
-
-function setScrollWidth() {
-  $('body').attr('data-scroll-width', getScrollWidth());
-}
+  },
 
-export {
-  getScrollWidth,
-  setScrollWidth,
+  setScrollWidth() {
+    $('body').attr('data-scroll-width', ScrollHelper.getScrollWidth());
+  },
 };
+
+export default ScrollHelper;

spec/javascripts/helpers/scroll_helper_spec.js

+import $ from 'jquery';
+import ScrollHelper from '~/helpers/scroll_helper';
+
+describe('ScrollHelper', () => {
+  describe('setScrollWidth', () => {
+    it('calls getScrollWidth and sets data-scroll-width', () => {
+      const width = 10;
+
+      spyOn($.fn, 'attr');
+      spyOn(ScrollHelper, 'getScrollWidth').and.returnValue(width);
+
+      ScrollHelper.setScrollWidth();
+
+      expect(ScrollHelper.getScrollWidth).toHaveBeenCalled();
+      expect($.fn.attr).toHaveBeenCalledWith('data-scroll-width', width);
+    });
+  });
+});