[1, 2, 3] | [1, 2, 3] | []        | []        | [1, 2, 3]
    }

    def "collect as map"() {
        expect:
        collectMap([1, 2, 3], transformer { it * 10 }) == [10: 1, 20: 2, 30: 3]
        collectMap([], transformer { it * 10 }) == [:]
    }

    def "collect values as map"() {
        expect:

    /**
     * Given a set of values, derive a set of keys and return a map
     */
    public static <K, V> Map<K, V> collectMap(Iterable<? extends V> items, InternalTransformer<? extends K, ? super V> keyGenerator) {
        Map<K, V> map = new LinkedHashMap<K, V>();
        collectMap(map, items, keyGenerator);
        return map;
    }

    }

    /**
     * Given a set of values, derive a set of keys and return a map
     */
    public static <K, V> Map<K, V> collectMap(Iterable<? extends V> items, Transformer<? extends K, ? super V> keyGenerator) {
        Map<K, V> map = new LinkedHashMap<K, V>();
        collectMap(map, items, keyGenerator);
        return map;
    }