Actually its already hacked i don’t have any problem with serial number and stuff wanted to know what things should i consider testing on console
I don't know what you mean be "testing on the console"; are you talking about Homebrew and games or physical hardware testing? Personally, I would check the following:
1) Firmware to see what games you can play (Ex: 4.x = no Smash Bros)
2) Are any of the efuses burnt, or have they been preserved? Also, is it running an emuNAND
3) Does the other person have a NAND backup(s)? I would still make my own ASAP, but if they made one before modifying the system, you have a 'clean' NAND copy to use with ChoiDujour in a worst-case scenario
4) Do they Joycons connect (if using your own) and do all the buttons work properly (if the deal includes them)? Do the analog sticks drift, are some buttons not as responsive as others, or do some buttons get stuck?
5) Does the system charge? Some people had third-party Switch docks that damaged the charging port, requiring repairs or 'alternative' charging methods
6) Do the power, volume +/-, game cartridge slot, and micro SD card slot work?