@Nonnull
    public static <K, V> BatchSource<Entry<K, V>> map(@Nonnull String mapName) {
        return batchFromProcessor("mapSource(" + mapName + ')', readMapP(mapName));
    }
@Test
    public void map_byRef() {
        // Given
        List<Integer> input = sequence(itemCount);
        putToBatchSrcMap(input);

        // When
        BatchSource<Entry<String, Integer>> source = Sources.map(srcMap);

        // Then
        p.readFrom(source).writeTo(sink);
        execute();
        List<Entry<String, Integer>> expected = input.stream()
                                                     .map(i -> entry(String.valueOf(i), i))
                                                     .collect(toList());
        assertEquals(toBag(expected), sinkToBag());
    }