```php
$graph = new Graph();
$graph->createVertex(1);
$graph->createVertex(2)->setGroup('A');

$alg = new Groups($graph);
var_dump($alg->getNumberOfGroups());
var_dump($alg->getGroups());
```

As a user, I'd expect to receive `(int)2` and 
```
NULL
string(1) "A"
```

I guess we may a different understanding here?