The attached project has a beanshell rule that should always succeed when you run maven install.
However, if you run it with multiple threads it sometimes fails. This shows that the evaluation of this beanshell rule is not thread-safe, although maven-enforcer-plugin claims to be thread safe.
Command to test it inside the base project (on a multi-core machine):
while mvn -T 2C clean install ; do sleep 1; done
This fails at some point sooner or later.