How to specify test directory in Maven pom.xml

Maven handles java unit tests well by defaulting to:

src/test/java

We're writing quite a few Groovy unit tests right now, and I'd like to find a way in Maven to specify a folder such as:

src/test/groovy

as a test folder. This would help us to import a Maven project into, say, IntelliJ, without additional setup.

Someone mentioned this was possible, but I wasn't able to find a way searching the Maven docs, or SO. Does anyone know how to mark the directory in the pom?

Thank you