Most beta tests for software have a non-disclosure agreement which often prohibits even stating one was part of any beta testing. If your agreements permit disclosure of the testing, then merely listing the software titles under beta testing would be sufficient.
I don't really know how much of a favorable impression it will relay, if any. Agreeing to run software and document problems with it is often not a job skill anyone is seeking. At least not for any kind of direct compensation. All software everywhere has beta testers... most often they work for free.
It's not like there are tests, requirements, or qualifications to be a beta tester. The only requirement is to be willing to document problems with the software. A beta testers proficiency level with the software can range from complete novice to seasoned experienced professional. Simply being a beta tester does not offer any credibility in most instances. Even if you were a beta tester for well-known, high-end, software, it just means you've used the software... but there's no telling how well you actually know the software.
If it were me, I'd not bother with any type of formal disclosure. I may casually mention it if the topic were to come up in conversation, but I certainly wouldn't do anything like adding it to a resume, bid, pitch letter, or web site. And yes, I could add such items myself, if I were so inclined.