fixed unhandled promise rejection

app/assets/javascripts/right_sidebar.js

@@ -75,12 +75,12 @@ Sidebar.prototype.toggleTodo = function(e) {
 
   $('.js-issuable-todo').disable().addClass('is-loading');
 
-  return axios[ajaxType](url, {
+  axios[ajaxType](url, {
     issuable_id: $this.data('issuable-id'),
     issuable_type: $this.data('issuable-type'),
   }).then(({ data }) => {
     this.todoUpdateDone(data);
-  });
+  }).catch(() => flash(`There was an error ${ajaxType === 'post' ? 'adding a' : 'deleting the'} todo.`));
 };
 
 Sidebar.prototype.todoUpdateDone = function(data) {

spec/javascripts/right_sidebar_spec.js

@@ -74,8 +74,7 @@ import Sidebar from '~/right_sidebar';
 
       it('should broadcast todo:toggle event when add todo clicked', function(done) {
         var todos = getJSONFixture('todos/todos.json');
-        spyOn(axios, 'get').and.callThrough();
-        mock.onAny(`${gl.TEST_HOST}/frontend-fixtures/issues-project/todos`).reply(200, todos);
+        mock.onPost(/(.*)\/todos$/).reply(200, todos);
 
         var todoToggleSpy = spyOnEvent(document, 'todo:toggle');