Characterizing a capacitive touchscreen
I could answer for a specific case, the laptop industry. In the (medium - large size device > 12" ), Microsoft has put in place a certification program, and in particular a process for Touch Device, certified by Microsoft lab, the WTTL. Each touch digitizer device must pass this certification to be qualified for windows 8.

Microsoft has defined a lot of tests, and as far as I experienced, the hardest test to pass is the Touch Paning Latency. Why ? Because one of the biggest challenge in touch digitizer is to achieve to get high accuracy and low latency at the same time.

A touch digitizer system basically acquires image of the touch panel, where area with fingers (palm, or ears) contrast with area with nothing. Image acquisitions are made at a given sampling rate. Then, image processing techniques like centroid detection localizes the center of finger(s).

Because signal's best ennemy is noise, filtering is needed there. So, based on averaging techniques could improve localization, and thus, accuracy. Averaging is taking time, because you need to accumulate data prior processing them. So, on one hand you could improve the accuracy in increasing the image averaging.

On the other hand, the more you do averaging, the more you increase latency. This is one of the well known compromise you have to do when you develop touch digitizers.

This is for the dynamic test. For the static test, one of the most stressful test is to put many fingers (supposing we are speaking about multi touch) horizontally or vertically on the touch panel. This is related to the grid effect of the capacitive structure. Which is why many of the very first demo were piano game, because only one dimension matters (vertical for example).  Of course, this is also valid only for capacitive touch panel.

Of course in your case you might not want to buy a robot for doing such paning latency test. But you could imagine having just one test where you draw a diagonal line, at a given speed, and capture the X, Y coordinates reported by the touch digitizer. But you need specific tools to make such test.