public function testUpdateWithSingleKey()
{
$doc = new Document(array('model' => $this->_model));
$result = MockDocumentPost::meta('key');
$this->assertEqual('_id', $result);
$doc->_id = 3;
$this->assertFalse($doc->exists());
$doc->sync(12);
$this->assertTrue($doc->exists());
$this->assertEqual(12, $doc->_id);
}