The Clover-for-Grails plugin allows you to produce Clover code coverage reports from the Grails web application development framework. It provides detailed information to highlight areas of low coverage in your project, helping to guide your unit-testing activities.
This plugin is open source, under the Apache 2.0 license. Source code is available here: https://bitbucket.org/atlassian/grails-clover-plugin
The plugin includes a built in 30-day evaluation license. You can buy full license here: https://my.atlassian.com/purchase
The easiest way is to define dependency to "clover" in your application's BuildConfig.groovy file. See installation guide for more details.
The latest binaries can be also downloaded from http://grails.org/plugin/clover page.