How might an internal auditor use an Integrated Test Facility in auditing a mortgage processing facility?

What are the major limitations of using an ITF?

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How might an internal auditor use an Integrated Test Facility in auditing a mortgage processing facility?

What are the major limitations of using an ITF?
I'm in no way trying to cheat on my homework. I just want to be sure that my thoughts are headed in the right direction. To substantiate this claim, here is what I came up with:

a. The auditor may create a dummy corporation as well as a few dummy customers and test the normal data at variable and fixed rates to determine its completeness and accuracy by comparing it with the auditor's own forecasted data.
b. The program would have to be specially modified which can be extremely costly; The exacting nature of the input that is required specifies that the information entered passes the decision rules before a transaction will be accepted; Removal of personnel from direct interaction with transactions, placing reliance on the system can cause a burden on control efforts which can allow costly mistakes to go uncorrected; Mixing test transactions with live data could cause a corruption of live data; Test transactions will have to be filtered out or reversed at a later date.

But hey, thanks anyway. I got a perfect score on my paper.