Is there a way to call a method of Main Application from UI Test Application

Help!

I faced a situation seem easy but not on UI Testing. The context is that from Testing UI's code, I want to call a method and retrieve output of it (or even not, just call).

For more specific, my context, I defined a method to capture screen in a Utility class, and from a UI test case, I want to take a screen shot and load it up to go further.

Is it clear enough and possible?