protected function setUp()
{
$this->directory_a = tempnam(sys_get_temp_dir(), 'tracked_files_unittest_a');
unlink($this->directory_a);
mkdir($this->directory_a);
$this->directory_b = tempnam(sys_get_temp_dir(), 'tracked_files_unittest_b');
unlink($this->directory_b);
mkdir($this->directory_b);
}