How do I use JUnit to test two classes (a client and a server) that both have main methods in Java?

How do I use JUnit to test two classes (a client and a server) that both
have main methods in Java?

I have a client class that uses a main function and a server class that
uses a main function. Junit won't let me use classes with a main function.
I can easily create the two classes without the main functions, but will
they both be able to run side by side???