UTP (Unit Test Plan) are done at smallest unit level or stand alone mode. Example you have Customer and invoicing module. So you will do test on Customer and Invoice module independently. But later when we want test both customer and invoice in one set we integrate them and test it. So thatâ€™s is SITP (System Integration Test Plan) UTP can be done using NUNIT. Unit testing is done normally by developers and System testing is done normally by testing department in integration mode.