@Test public void shouldGetMapEntryKeys() throws Exception { ArrayList<Entry<String, Integer>> list = createReverseOrderMapEntryList(); Comparator<Map.Entry<String, Integer>> comparator = ConvertingComparator.mapEntryKeys(new ComparableComparator<String>()); Collections.sort(list, comparator); assertThat(list.get(0).getKey(), is("a")); }