When you say you "logged," do you mean you logged it, or didn't log it?

You're correct: if you weren't a required crewmember under the regulation, it shouldn't be logged.

If you're submitting a resume, you can make a note under your employer details about your experience. Be careful not to represent it as flight experience when applying for a pilot job if you weren't involved in flying the aircraft. If you were on board taking flight data or monitoring systems, performance, etc, you can certainly say so or describe that experience (in a single sentence), but don't put or do anything that would misconstrue this or suggest you were doing something else (eg flying the aircraft) if you weren't.

You can also describe it in a cover letter. Remember that the cover letter is short and to the point, and the purpose is to get your foot in the door and get an interview; the interview is where you expand on things such as your flight test experience.

Likewise, in the actual job application, you can include a very brief description of your duties under your employment history with that employer.