grailstest.groovy

@TestFor(MyService)
class MyServiceSpec extends Specification {
  void "any test"(){    
    given:
    anotherService.xyz() >> 7
    
    when:
    Integer value = service.anyMethod()  
      
    then:
    value == 7
  }
  AnotherService anotherService = Mock(AnotherService)
  def setup(){
    service.anotherService = anotherService
  }
}

class MyService {
    AnotherService anotherService
  
  Integer anyMethod(){
    anotherService.xyz()
  }
}