[Haskell-beginners] Export two modules from one.hs file?

Hey  All, I currently want to make a module, which "truly" exposes 3 functions. However, there are more functions which I want to test. I would like to export two modules from the same file, "ModuleToUse" and "ModuleOpen". Then I can use ModuleToUse everywhere else, and ModuleOpen in the UnitTests. I know I can declare ModuleOpen, and export only certain functions with ModuleToUse. But I am not sure, if that is a smart / normal thing to do. In my case this would double my modules, and ... hence files? What is the "real world" approach for this? Thanks Leonhard