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).
There is already a goal to build a test jar from maven.
Assuming you need something a little more flexible, you can use the jar plugin to package your test resources and run that goal with the main package goal with something like this.
org.apache.maven.plugins
maven-jar-plugin
package
jar
test-resources
**/*.whatever-you-want
Whatever you want bundled would be added to the project-name-version-test-resources.jar when the jar goal is run.
You could then include it in a project via the same dependency you use above.