}

    def "adds to collection"() {
        def list = [0]
        when:
        addToCollection(addToCollection(list, [1, 2]), [2, 3])
        then:
        list == [0, 1, 2, 2, 3]
    }

    def "adds empty list to collection"() {
        expect:
        addToCollection([], []) == []
        addToCollection([1], []) == [1]
    }

    def "adds to collection preventing nulls"() {
        when:

            throw new IllegalArgumentException("args == null!");
        }
        args(Arrays.asList(args));
        return this;
    }

    public ProcessArgumentsSpec args(Iterable<?> args) {
        GUtil.addToCollection(arguments, true, args);
        return this;
    }

    public ProcessArgumentsSpec setArgs(List<String> arguments) {
        this.arguments.clear();
        args(arguments);
        return this;
    }

        add(Arrays.asList(values));
        return this;
    }

    /**
     * Adds some start nodes.
     */
    public CachingDirectedGraphWalker<?, ?> add(Iterable<? extends N> values) {
        GUtil.addToCollection(startNodes, values);
        return this;
    }

    /**
     * Calculates the set of values of nodes reachable from the start nodes.
     */
    public Set<T> findValues() {
        try {