public function canAquireEclusiveLock()
{
$file = vfsStream::newFile('foo.txt')->at($this->root);
$fp = fopen(vfsStream::url('root/foo.txt'), 'rb');
$this->assertTrue(flock($fp, LOCK_EX));
$this->assertTrue($file->isLocked());
$this->assertFalse($file->hasSharedLock());
$this->assertTrue($file->hasExclusiveLock());
fclose($fp);
}