Testing Classic ASP website deployed locally

Context: I am trying to code Tests using NUnit for a classic asp application deployed locally in my machine. This was developed 15 years ago and I am responsible for writing test cases to understand the possible outcomes of the certain workflow.

As part of rewriting this app in .NET, we are writing the tests

Given: All I have is a url http://ift.tt/1WaFF91

encryptedQueryString - this query string is valid only for few seconds/ milliseconds - this query string basically decides what type of output to expect

TODO

Write test cases to ping this URL with different encrypted querystrings and compare the output of that with a expected result file

Test cases should be configurable enough to plug and play various URL's

Appreciate any ideas / directions

Thanks