Ok, this configuration works for maven 2.
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>gmaven-plugin</artifactId>
<version>1.4</version>
<configuration>
<providerSelection>2.0</providerSelection>
<sourceEncoding>UTF-8</sourceEncoding>
</configuration>
<executions>
<execution>
<goals>
<goal>testCompile</goal>
</goals>
<configuration>
<sources>
<fileset>
<directory>${pom.basedir}/src/test/java</directory>
<includes>
<include>**/*.groovy</include>
</includes>
</fileset>
</sources>
</configuration>
</execution>
</executions>
</plugin>
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy</artifactId>
<version>2.0.0</version>
<scope>test</scope>
</dependency>