Julia - When developing a pacakge, how to use an specific dependence only on the test?

I'm developing Julia code for a package, and in my code, the user is free to choose the optimizer he wants, hence, my code does not depend on the many optimizers available. Yet, when I implemented a test set, and to check if the functions are indeed working I need to import an optimizer. My question is then, how to use an specific dependence only on the test? Without making it a dependency on the package itself?