public function testGc() {
$this->storage
->write('foo', 'bar');
$this->storage
->write('bar', 'foo');
$coll = self::$mongo
->selectDB($this->options['database'])
->selectCollection($this->options['collection']);
$this
->assertEquals(2, $coll
->count());
$this->storage
->gc(-1);
$this
->assertEquals(0, $coll
->count());
}