How to mock server.mappath for running in NUnit?

Split off from http://forums.asp.net/t/1656547.aspx/1?Render+XML+ as it contained a totally new question:
Hi Thanks for the reply. I managed to write code to render the xml using MVC. My controller loads the xml document and using xslcompiledtransform, tranform the xml and return the string to the browser. Everything is fine upto this. Now the problem comes when i run the NUnit test. Because i am using Server.Mapth(... for loading the xml and xslt, the nunit throwing the error. Can anyone please help me how to mock the server.mappath for runnign nunit. thanks
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