Anybody can be the Scrum Master, just make sure the Scrum Master has no other conflict of interest roles as Product Owner, Manager or Stakeholder.
Personally I think testers have the potential to be great Scrum Masters, because:
- Testers discover problems/defects, but often do not demand a certain solution. Its up-to the owners of the issue to find the best solution. This places us already in a sort of servant leader situation, which could lead to team to accept findings from a tester more easily then from a manager or a co-developer.
- Focus on quality, also in processes. As testers often have a broader role. From requirements till deployment. Getting people out of their silos might be easier if you understand the full process end2end.
- Continuous improvement should already by a part of your job, how do you prevent defects from reoccurring. This could also be applied to other parts of the SDLC.
- Testers should be better at communication with different roles then for example developers. Since they have more interaction when escalating quality issues and or trying to reproduce issues. Testers should be able to communicate with Users, Managers, Developer and Stakeholders in their own language. Where most developers are just to technical and traditional project managers are not at all technical.
This are just somethings that come to mind. Getting the certification might be good reason for a team to let you try the Scrum Master role for a while in an existing team.
If your company already uses Scrum doing the certification is a good idea anyways. Understanding and improving your Scrum knowledge is good for any member of a Scrum team, I would advice anyone on a Scrum team to do a training, read a good Scrum book and or do the certifications.