Running unit tests when Volley is being used as a submodule

I'm writing my first unit tests for my application, and when I switch the build variant to Unit Tests, Volley's tests blows up and says that Junit isn't imported.. I could import it in the app module build.gradle, but I don't know how to do that to resolve the errors for Volley? I don't care about the tests for Volley, just my own. How can I fix it?

Thank you!