There is a clear solution for sharing the common test code between maven projects using test-jar goal of maven-jar-plugin plugin (see here).
Just use jar:test-jar and declare the resulting JAR as a dependency (refer to this guide for more details). And while I don't understand the problem of having resources and classes in this jar, you can always exclude all .class files:
org.apache.maven.plugins
maven-jar-plugin
2.2
test-jar
**/*.class
And to use it:
...
com.myco.app
foo
1.0-SNAPSHOT
test-jar
test
...