If case you want to test or build only a project (sub module) you have several options since Maven 2.1
This example maven project has sub module which generates an rpm package.
coolapp |-- api |-- impl |-- db |-- ear |-- deploy |-- rpm |-- deb |-- osgi
Invoking the maven goal
rpm:rpm applies only to the project rpm. Invoking on path coolapp
mvn rpm:rpm --projects deploy/rpm # short form mvn rpm:rpm -pl deploy/rpm
If you want to also build dependencies
mvn rpm:rpm --projects --also-make deploy/rpm # short form mvn rpm:rpm -pl -am deploy/rpm
Take also a look at advanced reactor options.