Added more notes about testing

Author: ysb33r

HACKING.md

@@ -8,7 +8,12 @@ Unit tests are in 'src/test' and integration tests are in 'src/integTest'. To ru
 do `./gradlew check` or `./gradlew build`. For unittests just doing `./gradlew test` is enough.
 
 Test logging is controlled via `logback-test.xml`. Be aware that integration tests generate a lot of debug information.
-Please do not commit the config file back with DEBUG turned on
+Please do not commit the config file back with DEBUG turned on.
+
+=== Running single test suites
+
+If you only want to run the unittests in say `JRubyPlugin` then you can do `./gradlew test -Dtest.single=JRubyPlugin`.
+In a similar manner for integration tests one can do `./gradlew integrationTest -Dtest.single=JRubyIntegrationSpec`.
 
 == Release HOWTO