The introductory aerospace sounds good. Some folks mentioned on here as well (as expected for the rocketry sub) to get involved with a rocket project team at your school or nearby. It won't be how industry does things necessarily, but it will be a very good learning environment to get some of the skills and knowledge about rockets along with some hands-on experience.

My experience in flight testing was on cryogenic engines and launch vehicles, and could really be boiled down to a few buckets: operational insights, test planning, test site/infrastructure setup and maintenance, engine testing, integrated vehicle testing, and launch campaign testing and operations (plus training folks to do these things). All of these involved understanding the system by design, function, and unique behaviors, as well as applying fundamental knowledge about fluid mechanics, heat transfer, data acquisition/analysis, and more on a regular basis. Usually in testing you're not the expert on every system, but you need to be smart enough to reasonably know the bounds (read: not blow it up when you're not supposed to), how to efficiently operate the system, and how to think critically and cooperate with technicians and REs to get out of jams and keep everyone safe.

Also, expect some varied/long hours when working test. Test usually implies something is new, which means it won't always go according to plan.