for (K key : keysToTest) {
      assertEquals(expected.lowerEntry(key), navigableMap.lowerEntry(key));
      assertEquals(expected.floorEntry(key), navigableMap.floorEntry(key));
      assertEquals(expected.ceilingEntry(key), navigableMap.ceilingEntry(key));
      assertEquals(expected.higherEntry(key), navigableMap.higherEntry(key));

    }
    {
      Entry<Integer, String> entry = unmod.lowerEntry(1);
      assertThat(entry).isNull();
    }
    {
      Entry<Integer, String> entry = unmod.floorEntry(2);
      assertThrows(UnsupportedOperationException.class, () -> entry.setValue("four"));
    }
    {
      Entry<Integer, String> entry = unmod.ceilingEntry(2);