If at the end of the run the seat count is reduced by exactly 2000 seats, you pass.
However if there wern't 2000 seats to begin with, and you end up with 2000 seats being booked then either you failed or your test scenario wasn't quite right
You probably need to test the locking mechanism, which would require you to have the business logic in the threads - lock a record / confirm number of seats available / decrement count / unlock record (if you have implemented the business logic at the client side not the server side).
You could then try starting with an initial seat count of 3999, reducing by two seats at a time. At the end of the run, one of your threads should have complained that there were not enough seats available, and
you should have one seat left in the table.
The tests can get far more involved than this as well