Sokil\Mongo\Collection::getDocumentByReference PHP Method

    public function getDocumentByReference(array $ref, $useDocumentPool = true)
    {
        $documentArray = $this->getMongoCollection()->getDBRef($ref);
        if (null === $documentArray) {
            return null;
        }
        return $this->hydrate($documentArray, $useDocumentPool);
    }

 public function testGetDocumentByReference()
 {
     // create document
     $document = $this->collection->createDocument(array('param' => 'value'))->save();
     // invalid col and db
     $foundDocument = $this->collection->getDocumentByReference(array('$ref' => 'some_collection', '$db' => 'some_db', '$id' => $document->getId()), false);
     $this->assertNull($foundDocument);
     /// invalid db
     $foundDocument = $this->collection->getDocumentByReference(array('$ref' => $this->collection->getName(), '$db' => 'some_db', '$id' => $document->getId()), false);
     $this->assertNull($foundDocument);
     // all valid
     $foundDocument = $this->collection->getDocumentByReference(array('$ref' => $this->collection->getName(), '$db' => $this->collection->getDatabase()->getName(), '$id' => $document->getId()), false);
     $this->assertSame((string) $document->getId(), (string) $foundDocument->getId());
 }