@Test
public void testZipKeysWithValueFunc() {

    final Map<String, Integer> lengths = Stream.of("foo", "bar", "acme", "baboon")
            .collect(Collectors.toMap(Function.identity(), String::length));
    final Map<String, Integer> collected = Stream.of("foo")
            .map(zipKeysWithValueFunc(lengths::get))
            .collect(Fun.entriesToMap());
    assertEquals("zipKeys map should match", Collections.singletonMap("foo", 3), collected);
}