The only way to be 'tested' as exchange is to have hackers fail to steal coins or information from you. If they manage to steal one of these or both, you obviously failed because your exchange wasn't secure enough.

Some exchanges tend to not publicly share that they have been hacked, but a red flag would be that they don't or barely process withdrawals, which is an indication of insolvency.

Either way, if you want to try out an exchange, try to deposit like a buck worth of Bitcoin or any other coin to see if you can withdraw without problems. If they are a scam, you only lost a buck, which isn't the end of the world.