gsjava org.junit cannot be resolved

1. Command line: In the case of command line invocations, you will have to add junit.jar to the classpath of your application with java -cp /path/to/junit.jar. Take a look at the answers here.

2. Using eclipse: Eclipse distributions are bundled with this library and this is how you can use it for your project. Right click on the eclipse project and navigate:

Properties -> Java Build Path -> Libraries -> Add Library -> JUnit -> Junit 3/4