Hi Hajlaouijalel Hajlaoui,

Hope you are fine... based from my understanding on SaaS and BPaaS, BPaaS is any type of business process that delivered based on cloud services model. From here we know that cloud services model are  included SaaS, PaaS and also IaaS depend on what kind of related services. 

As to answer your question, testing and validation done will be based from what type of services. Here is one article that relate with challenges of SaaS Testing for your further reading and info. Sorry can not give lots of input coz still new and need to do more reading in this area... Hope it can help you a lot.  :)