Create a sanbox of 20 users where the tests can be run prior to being committed to the real test.

Actually Blazemeter has a sandbox that allows users to run the script prior to committing it to the actual load - it is a  free low-scale test for debugging purposes.   I suppose the playback would be considered a sandbox that finds object errors.    I can always go back to using JMeter.   I was able to run the script all the way through and validate the data prior to committing it to the cloud.