To me drug tests do not mean that much.
Overroid passed his tests before the fight with Lesnar. He said that he was clean and agreed to random testings during 2012. At the end he got caught.
Obviously if Lombard is tested now he will be clean (he is not stupid to ask for drug test if he knows he will piss dirty). That does not mean that he has never taken any stuff or that he will never do that again.
I am not saying that he is or was in roids. Maybe he is or maybe he is not.
The thing is that it is not a secret that many fighters use illegal stuff. Just very few of them get caught.