I assume you test in the production environment.

Or, you have a test environment that:

• Duplicates all the Production System's configurations and databases exactly.
• Duplicates loading and all external interface interaction with the Production System exactly.
• Has exactly the same hardware as your production system.
• Has a parallel set of operation's people performing exactly the same operations on it.

Oh, and while you are at it, how do you setup a test environment that's exactly like the production environment when the test environment has additional loading from the program under testing? Which is why I assume you must be testing in production.

The fact is, differences between your test and production environments cannot _introduce_ new bugs into a program, only exhibit bugs that are inherent in the program that are expressed in different environments.