Software

• Groovy Eclipse compiler (2.9.2.xx-201508121448-e45)
• Eclipse Mars (4.5.1 20150924-1200)
• Grails 3.1.0.M2

Steps

• Generated a unit test in on the command-line in my project with create-domain-class Sample
• This also generates a SampleSpec which looks like

package test.Sample

import grails.test.mixin.TestFor
import spock.lang.Specification

/**
 * See the API for {@link grails.test.mixin.domain.DomainClassUnitTestMixin} for usage instructions
 */
@TestFor(Sample)
class Sample extends Specification 

• Refreshed the project in Eclipse. Now there's a red cross before the "package ..." line with an errror: Groovy:Could not find class for Transformation Processor org.grails.compiler.injection.test.TestForTransformation declared by grails.test.mixin.TestFor