Use the Db get helper rather than always Tracker DB, this could fix an issue in tests

core/Tracker/Model.php

@@ -11,6 +11,7 @@ namespace Piwik\Tracker;
 use Exception;
 use PDOStatement;
 use Piwik\Common;
+use Piwik\Db;
 use Piwik\Tracker;
 use Piwik\Tracker\Db\DbException;
 
@@ -377,7 +378,7 @@ class Model
 
     private function getDb()
     {
-        return Tracker::getDatabase();
+        return Db::get();
     }
 
 }

tests/PHPUnit/bootstrap.php

 <?php
 define('PIWIK_TEST_MODE', true);
-define('PIWIK_PRINT_ERROR_BACKTRACE', true);
+define('PIWIK_PRINT_ERROR_BACKTRACE', false);
 
 if (!defined("PIWIK_PATH_TEST_TO_ROOT")) {
     define('PIWIK_PATH_TEST_TO_ROOT', realpath(dirname(__FILE__) . '/../..'));