Groovy closure delegation test

gistfile1.groovy

import spock.lang.Specification

class ClassInstanceAccessFromWithinClosureSpec extends Specification {
    def component = new ClassUnderTest()

    def "class instance variable is accessible when called from within closure delegated to Object" (){
        setup: def delegate = new Object()
        expect: component.execute(delegate)
    }

    def "class instance variable is accessible when called from within closure delegated to String" (){
        setup: def delegate = 'delegate'
        expect: component.execute(delegate)
    }

    def "class instance variable is accessible when called from within closure delegated to Closure" (){
        setup: def delegate = {}
        expect: component.execute(delegate)
    }

    def "class instance variable is accessible when called from within closure delegated to Integer" (){
        setup: def delegate = 1
        expect: component.execute(delegate)
    }

    def "class instance variable is accessible when called from within closure delegated to Map" (){
        setup: def delegate = new HashMap()
        expect: component.execute(delegate)
        // Throws NPE
    }

    def "class instance variable is accessible when called from within closure delegated to List" (){
        setup: def delegate = new ArrayList()
        expect: component.execute(delegate)
        // Throws groovy.lang.MissingMethodException
    }

    def "class instance variable is accessible when called from within closure delegated to Collection" (){
        setup: def delegate = Mock(Collection)
        expect: component.execute(delegate)
        // Throws NPE
    }

}

class ClassUnderTest {
    def speaker = [speak:{println "Hello"}]
    def execute(delegate) {
        speaker.speak()
        delegate.with {
            speaker.speak()
        }
        true
    }
}