def ref = registry.atState("ref", ModelNode.State.Discovered)

        when:
        ref.setTarget(newTarget)

        then:
        IllegalStateException e = thrown()
        e.message == "Cannot set target for model element 'ref' as this element is not mutable."

        where:
        newTarget << [null, Stub(MutableModelNode)]
    }

    def "rules are invoked in order before element is closed"() {

// variable of an assignment, or of a function result variable.
type target struct {
	sig  *Signature
	desc string
}

// newTarget creates a new target for the given type and description.
// The result is nil if typ is not a signature.
func newTarget(typ Type, desc string) *target {
	if typ != nil {
		if sig, _ := under(typ).(*Signature); sig != nil {
			return &target{sig, desc}
		}
	}

// variable of an assignment, or of a function result variable.
type target struct {
	sig  *Signature
	desc string
}

// newTarget creates a new target for the given type and description.
// The result is nil if typ is not a signature.
func newTarget(typ Type, desc string) *target {
	if typ != nil {
		if sig, _ := under(typ).(*Signature); sig != nil {
			return &target{sig, desc}
		}
	}