I am writing unit tests for a class, and two methods in the class accepts an answer from the UI. The tests run smooth but a UI element is called every time the test runs and I would have to click the message box manually and run the tests. I need to find a way to run the tests without calling the UI element. Is there a feature in the NUnit test framework to not invoke any UI functions?

I passed an extra boolean into the method just for the purpose of testing but my supervisor told me that was not ideal and I have to find another way to do it.