fix tests

tests/lib/testcase.php

@@ -174,8 +174,10 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase {
 		\OC\Files\Filesystem::tearDown();
 		\OC_User::setUserId($user);
 		\OC_Util::setupFS($user);
+		if (\OC_User::userExists($user)) {
 			\OC::$server->getUserFolder($user);
 		}
+	}
 
 	/**
 	 * Logout the current user and tear down the filesystem.