Need help how to manage a couple of daily DB copies.

Hi,

I'd like to set up a DB-Server that keeps copies of our productive db
for an external db-assistant.
He should prepare chores on the test-server and mail the sql scripts to me.
I'll look over those scripts and run them against the productive db myself.

So I'd like to have a daily cron job dump the main db, rename the
test-db to something with a date in it.
Like test_db --> test_db_20131024
Create a new test_db and import the dump of the main db.

So far no problem but how could I limit the number of test_dbs to 5?
I'd like to keep those test_dbs 5 days and then drop them.