or

inside BuildConfig.groovy as part of grails.project.dependency.resolution

plugins {
     //note that the version used might not reflect the latest version available
     test("org.grails.plugins:geb:0.6.0")
}

For further reference please review the instructions here

Geb is a browser automation solution.

It brings together the power of WebDriver, the elegance of jQuery content selection, the robustness of Page Object modelling and the expressiveness of the Groovy language.

It can be used for scripting, scraping and general automation — or equally as a functional/web/acceptance testing solution via integration with testing frameworks such as Spock, JUnit & TestNG.

The Book of Geb contains much of the information you need to get started with Geb.

An example application with spock tests exists here Geb-example-grails. Grab it for reference and also make sure to check out the BuildConfig.

You can view and contribute to Geb via github: https://github.com/geb/geb