NO IRS does not do test deposits.
Did you get a tiny refund?
Then, IRS adjusted away most of what you thought you would get as a refund.
What do you mean a test?
All transactions processed through the ACH system involve several steps that include verifying the account information and the availability of funds by the sending bank and the account information of the receiving bank account holder. If the name, SSN and account number of the taxpayer provided by the sending bank (the IRS) does not match the information of the receiving bank, the receiving bank has the option of bouncing the deposit. However, that's up to the policies of the receiving bank. If you direct money into an account with the wrong number, or an account belonging to someone else (either accidentally or on purpose), the IRS is not liable if the deposit is completed but you can't get your funds. You would have to discuss the matter with your bank. If the receiving bank bounces the funds, the IRS will mail a check.
The IRS does have some anti-fraud measures, but they aren't publicly disclosed. We have seen occasionally where the IRS will mail a paper check even though the bank account number provided was valid. We can guess this might be related to anti-fraud protection, but we don't know for sure.
The IRS does not have any publicly acknowledged procedure to verify when a taxpayer changes bank accounts, other than the normal procedures that are part of every ACH transaction.