You could attach the test JAR to your build. Then both the test JAR and app JAR would be in the repository.
I can think of two ways to do this:
1) Set a finalName for the test JAR within the jar:test-jar plugin properties using something like "${project.build.finalName}_tests" and then use the Build Helper plugin (
http://mojo.codehaus.org/build-helper-maven-plugin/) to attach the test JAR to the build.
2) Modify the Jar plugin to add an attach option and a classifier option. Actually, I'm rather surprised that these options don't already exist. I can think of some cases where tests for one project would like to depend on tests for another project, especially of those projects are related. I would then submit this patch back to the community.
If I had to do this, I would opt for option 2.