public function testLock()
 {
     $backend = new ezcWebdavMemoryBackend();
     $backend->options->lockFile = $this->tmp . 'backend.lock';
     $backend->lock(1000, 200000);
     $this->assertFileExists($backend->options->lockFile, 'Lock file not created');
     $backend->unlock();
     $this->assertFileNotExists($backend->options->lockFile, 'Lock file not removed.');
 }