}

    def "cannot add elements after collection is realized"() {
        given:
        container.add(Stub(SwiftBinary))
        container.realizeNow()

        when:
        container.add(Stub(SwiftBinary))

        then:
        def e = thrown(IllegalStateException)
        e.message == 'Cannot add an element to this collection as it has already been realized.'
    }

        @Override
        public void collectInto(ImmutableCollection.Builder<T> builder) {
            if (!realized) {
                realize();
            }
            builder.addAll(cache);
        }

        List<T> getValues() {
            if (!realized) {
                realize();
            }
            return cache;
        }

        public boolean remove(T value) {

        }
        elements.add(element);
    }

    /**
     * Realizes the contents of this collection, running configuration actions and firing notifications. No further elements can be added.
     */
    public void realizeNow() {
        if (state != State.Collecting) {

        // Realize all object of type `type`
        def element = container.withType(type).iterator().next()

        when:
        def didRemoved = container.remove(element)

        then:
        didRemoved

        and:
        0 * _
    }

    def "will execute remove action when removing external provider only for realized elements"() {

            // Collect elements discarding potential side effects aggregated in the returned value
            collector.collectInto(builder);
            List<T> realized = builder.build();
            for (T element : realized) {
                doAddRealized(element);
            }
        }
    }

    private void doAddRealized(T value) {
        if (values.add(value) && addRealizedAction != null) {

public interface ElementSource<T> extends Iterable<T>, WithEstimatedSize, PendingSource<T>, WithMutationGuard {
    /**
     * Iterates over and realizes each of the elements of this source.
     */
    @Override
    Iterator<T> iterator();

    /**
     * Iterates over only the realized elements (without flushing any pending elements)
     */
    Iterator<T> iteratorNoFlush();

    /**

            tasks.register("bar", Delete)
        """

        when:
        succeeds "help"

        then:
        // help task is realized and configured
        outputContains("configured :help")

        // are "built-in" tasks realized and configured?
        if (realizesBuiltInTasks) {
            outputContains("configured :tasks")
            outputContains("configured :projects")
        } else {

                doLast {
                    assert defaultTaskRealizedCount == 0, "All DefaultTask shouldn't be realized"
                    assert zipTaskRealizedCount == 1, "All Zip task should be realized"
                }
            }
        '''

        expect:
        succeeds "foo"
    }

    def "realizes only the task of the given type when verifying if a filtered task collection is empty"() {
        buildFile << '''

        and:
        source.iterator().collect() == iterationOrder("foo", "bar", "baz", "fizz", "fuzz", "bazz")
    }

    def "once realized, provided values appear like realized values"() {
        when:
        source.addPending(provider("foo"))
        source.add("bar")
        source.add("baz")
        source.addPending(provider("fizz"))

        source.contains("foo")
    }

    def "an element added as both a provider and a realized value is not duplicated"() {
        when:
        source.add("foo")
        source.addPending(provider("foo"))

        then:
        source.iterator().collect() == ["foo"]
    }

    def "an element added as both a provider and a realized value has the correct order"() {
        when:
        source.addPending(provider("foo"))