@Nonnull
    public static <K, V> BatchSource<Entry<K, V>> map(@Nonnull String mapName) {
        return batchFromProcessor("mapSource(" + mapName + ')', readMapP(mapName));
    }
@Test(expected = IllegalStateException.class)
    public void when_batchSourceUsedTwice_then_throwException() {
        // Given
        BatchSource<Entry<Object, Object>> source = Sources.map(srcName);
        p.readFrom(source);

        // When-Then
        p.readFrom(source);
    }