We should use UserID object to identify users instead of username.

ash/test/test_session_state_delegate.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/test/test_session_state_delegate.h"
 
 #include <algorithm>
 #include <string>
 
 #include "ash/shell.h"
@@ skipping 213 matching lines @@
 
 const user_manager::UserInfo* TestSessionStateDelegate::GetUserInfo(
     content::BrowserContext* context) const {
   return user_list_[active_user_index_];
 }
 
 bool TestSessionStateDelegate::ShouldShowAvatar(aura::Window* window) const {
   return !GetActiveUserInfo()->GetImage().isNull();
 }
 
-void TestSessionStateDelegate::SwitchActiveUser(const std::string& user_id) {
+void TestSessionStateDelegate::SwitchActiveUser(const user_manager::UserID& user_id) {
   // Make sure this is a user id and not an email address.
-  EXPECT_EQ(user_id, GetUserIDFromEmail(user_id));
+  EXPECT_EQ(user_id.GetUserEmail(), GetUserIDFromEmail(user_id.GetUserEmail()));

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:46]

No need for this check here. This check should be done at UserID creation time.

   active_user_index_ = 0;
   for (std::vector<MockUserInfo*>::iterator iter = user_list_.begin();
        iter != user_list_.end();
        ++iter) {
     if ((*iter)->GetUserID() == user_id) {
       active_user_index_ = iter - user_list_.begin();
       return;
     }
   }
   NOTREACHED() << "Unknown user:" << user_id;
 }
 
 void TestSessionStateDelegate::CycleActiveUser(CycleUser cycle_user) {
-  SwitchActiveUser("someone@tray");
+  SwitchActiveUser(user_manager::UserID(std::string(), "someone@tray"));

[Denis Kuznetsov (DE-MUC), 2015/06/10 16:50:46]

FromUserEmail()

 }
 
 bool TestSessionStateDelegate::IsMultiProfileAllowedByPrimaryUserPolicy()
     const {
   return true;
 }
 
 void TestSessionStateDelegate::AddSessionStateObserver(
     SessionStateObserver* observer) {
 }
 
 void TestSessionStateDelegate::RemoveSessionStateObserver(
     SessionStateObserver* observer) {
 }
 
 }  // namespace test
 }  // namespace ash