A mechanism for testing a database transaction system without modifying a database is provided. A transaction commit instruction, sent by a transaction manager, is intercepted. The transaction commit instruction is intended to instruct a database driver to cause a transaction to be committed. The transaction commit instruction is prevented from reaching the database. A failure signal is sent back to the transaction manager to indicate a failure to commit the transaction even though the database has not experienced the failure. This enables a failure to be simulated without causing a database to suffer any adverse effects.