you add the script to run in your bitcoin.conf:

blocknotify= %s
walletnotify= %s
alertnotify= %s

and when blocks or notifications come in the script will be called with arguments.

for example if you use blocknotify the argument will be the block id e.g. 000000000000000003a5ff0d28a8f9b71623c2328727937160582d1b44cb3cec, if you use walletnotify then the argument will be the new transaction id that came in, e.g. 1e621e60f7ea7195ff1ec7c31867dc7c9d896123ead6ec43f053f51137c31676

make yourself a script (python or your favorite language) that logs the arguments somewhere and test it out with the scenarios you want.