Fix files_external tests

Signed-off-by: Joas Schilling <coding@schilljs.com>

apps/files_external/tests/Service/UserGlobalStoragesServiceTest.php

@@ -64,7 +64,7 @@ class UserGlobalStoragesServiceTest extends GlobalStoragesServiceTest {
 
 		$this->globalStoragesService = $this->service;
 
-		$this->user = $this->createMock(IUser::class);
+		$this->user = new \OC\User\User(self::USER_ID, null, \OC::$server->getEventDispatcher());
 		/** @var \OCP\IUserSession|\PHPUnit_Framework_MockObject_MockObject $userSession */
 		$userSession = $this->createMock(IUserSession::class);
 		$userSession