def action = Mock(Action)
        container.beforeCollectionChanges(action)

        when:
        container.add("a")

        then:
        1 * action.execute(null)
        0 * _
    }

    def objectIsNotAddedWhenVetoActionThrowsAnException() {
        def action = Mock(Action)
        def failure = new RuntimeException()
        container.beforeCollectionChanges(action)

        when:
        container.add("a")

import org.gradle.api.Action;

/**
 * A {@link MutationValidator} that can be used as a {@link Runnable} to be passed to
 * {@link org.gradle.api.internal.DefaultDomainObjectSet#beforeCollectionChanges(Action)}.
 */
public abstract class RunnableMutationValidator implements MutationValidator, Runnable {
    private final MutationType typeAsRunnable;

     *
     * assertMutableCollectionContents is only used by add/remove methods, but we should remove this special handling and fix
     * DefaultConfiguration and CompositeDomainObjects.
     */
    public void beforeCollectionChanges(Action<Void> action) {
        beforeContainerChange = beforeContainerChange.add(action);
    }

    @Override
    protected void assertMutableCollectionContents() {
        beforeContainerChange.execute(null);

        this.ownDependencies.beforeCollectionChanges(validateMutationType(this, MutationType.DEPENDENCIES));
        this.ownDependencyConstraints = (DefaultDomainObjectSet<DependencyConstraint>) domainObjectCollectionFactory.newDomainObjectSet(DependencyConstraint.class);
        this.ownDependencyConstraints.beforeCollectionChanges(validateMutationType(this, MutationType.DEPENDENCIES));