If you don't have the budget enough to buy an ESD "gun", you can make it by yourself, exclusively in order to verify the quality of your Printed Circuits.

Take a gas-lighter, get rid of the advanced metallic cap of protection, connect to the inferior metallic part a crocodile. This will be your pseudo-earth. On the tip of the gas-lighter, connect a sturdy point to help the discharge.

Your homemade ESD "gun" is ready.

PAY ATTENTION NOT TO GET SHOCKED, USING IT WITH CAUTION!!!

Some tests that you can make (beyond those described in the previous post) are:

Connect the crocodile to the mass of your printed circuit, connect a cable on the terminal board of your PCB (example the RS485 line), try to discharge the "gun" tip on the cable and verify that the discharge, if it happens, it is limited in the zone near the terminal board, or however where You have previewed.
In Your tests consider a distance of 1mm for a discharge of ~4KV
If you have the discharge in a faraway point from the terminal board, even on the mass pin of the microprocessor...perhaps there is something that does not go in the criteria with which it has been made the PCB.

Obviously this is only an empirical test, but for sure it's a valid answer (economic and fast) in order to verify the correct positioning of the tracks in a printed circuit. Therefore if you must certify a product, second ESD tests, you will have necessarily to go in a CE laboratory, equipped with instruments of programmable discharge ex. 4KV , 8KV.

If the Protection Device book interests you, it can be found on the ST site --->> www.st.com

Go to the Protection LINKS and RESOURCES --->>> EMI/RFI & TELECOM Protections