intro to grails 3 Testing
Channel: Boston Groovy Grails & Spring Meetup
Date: 2016-05-30

In this video I use the unit test generated from the enforcer plugin to demonstrate some of the testing you can do in grails. To go deeper I would checkout the Spock framework, which is used for Grails testing.
http://spockframework.github.io/spock/docs/1.0/index.html