If the "usb flash drive" means typical USB stick, then there is nothing to check. It is typical fully electronic microprocessor and it if works or not. There is no other way, that means like half works and the other half doesn't. If it doesn't work no more, there is no way to fix anything. Principe is simple - 1 or 0.
No, I don't think so, the world is full of "wise men", of all kinds. But it is true, there is nothing to control.
H2testw H2testw is able to test USB flash drives, memory cards and also internal, external and even network hard drives for errors.
I had the impression that the OP was concerned about something malicious on the drive. Seeing that getting a small 4 gb drive would not be worth the trouble because you can get a good 16gb drive for under $10. today. If the drive may be suspicious then give it a toss and replace as Mr X suggested
I can recall a story I heard a few (well maybe more than "a few") years ago, but a bank hired an IT security company to test the penetration security of this bank. What they did was to drop off a couple of usb drives in the parking lot before the bank opened. Sure enough some employees picked up those drives and the bank's security was breached. I can't recall the name of the security company that did this but they were successful in hacking this bank.