The Modernized e-File (MeF) programs go through several stages of review and testing before they are used to process live returns.  When new requirements and functionality are added to the Assurance Testing System and the Production System, testing is performed by IRS' software developers and by IRS' independent testing organization. These important activities ensure that the electronic return data can be received and accurately processed by MeF systems. Every time an IRS tax form is changed and affects the XML schema, the entire development and testing processes are repeated.