My cats like testing string. They are free to good home if you pay shipping. They don't store any readings, but they will sit in your lap if you are reading. They tend to push your book if you don't pet them.
Not a lot of choices out there. Seaward and Solmetric on the small end of the scale. There are testers that will let you test whole combiner boxes at a time and those are in the $30,000 range. Needed on utility scale projects.
Unfortunately setups which can run an I-V curve on single cells or panels are in a different ballpark from those which can run the same curve on a full string, because of the much higher power dissipation required of the test load when working with a full string. Also voltages can exceed 1000V.