There is a class loader issue when using Gmock with @Grab. So the following script will fail with a CodeGenerationException caused by ClassNotFoundException of org.gmock.internal.cglib.proxy.Factory:

@Grab('org.gmock:gmock:0.8.0')
import org.gmock.GMockTestCase

class GMockWithGrabTest extends GMockTestCase {
    void testMock() {
        def m = mock() // throws a CodeGenerationException
        m.fun()
        play {
            m.fun()
        }
    }
}

We have to config grape to use system class loader as below:

@Grab('org.gmock:gmock:0.8.0')
@GrabConfig(systemClassLoader = true)
import org.gmock.GMockTestCase

class GMockWithGrabTest extends GMockTestCase {
    void testMock() {
        def m = mock() // mocks successfully
        m.fun()
        play {
            m.fun()
        }
    }
}