Run "traditional" unit test in Nightwatch

I have a couple of utility functions, like validateEmail(email) that I would like to test directly, that is, without going through the UI. Is that possible through Nightwatch? I have all my UI testing in Nightwatch, and would like to stick with a single toolset for all my testing. And yes, I "get it" that most testing can (and perhaps should) be at the "public" level. But for completeness I also like to directly test some internal utility functions with every conceivable input. Thanks!