Testerpresent is just a dumb service which is responding with a constant. Its comparable with the "ping-service" on the internet. its just being used for checking by testers if the ECU is online. OEM implementation is always the same, and does not have any "extended" functionality.

That being said, its been common practise for alot of custom-code-devs to "sneak-in" some advanced services into this service. The code responsible for testerpresent is usually really easy to find and does not change (much) over different ecu variants. The functionality implemented depends on whatever has been patched into the binary. I personally use it for memory-read, memory-write, memory-execute. However any kind of functionality can be implemented, so unless you provide a binary, nobody can exactly tell you what exactly may or may not be triggered there.