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Parallel/audit testing is testing where the user reconciles the output of the new system to the output of the current system to verify the new system performs the operations correctly. Let us say, for example, the currently software is in the mainframe system which calculates the interest rate. The company wants to change this mainframe system to web-based application. While testing the new web based application, we need to verify that the web-based application calculates the same interest rate. This is parallel testing.