private Range<K> coalescedRange(Range<K> range, V value) {
    Range<K> coalescedRange = range;
    Entry<Cut<K>, RangeMapEntry<K, V>> lowerEntry =
        entriesByLowerBound.lowerEntry(range.lowerBound);
    coalescedRange = coalesce(coalescedRange, value, lowerEntry);

    Entry<Cut<K>, RangeMapEntry<K, V>> higherEntry =
        entriesByLowerBound.floorEntry(range.upperBound);

  private Range<K> coalescedRange(Range<K> range, V value) {
    Range<K> coalescedRange = range;
    Entry<Cut<K>, RangeMapEntry<K, V>> lowerEntry =
        entriesByLowerBound.lowerEntry(range.lowerBound);
    coalescedRange = coalesce(coalescedRange, value, lowerEntry);

    Entry<Cut<K>, RangeMapEntry<K, V>> higherEntry =
        entriesByLowerBound.floorEntry(range.upperBound);

      assertTrue(Thread.holdsLock(mutex));
      return delegate().lastEntry();
    }

    @Override
    public @Nullable Entry<K, V> lowerEntry(K key) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().lowerEntry(key);
    }

    @Override
    public @Nullable K lowerKey(K key) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().lowerKey(key);
    }

  }

  <K, V> void testNavigationAgainstExpected(
      NavigableMap<K, V> expected, NavigableMap<K, V> navigableMap, Iterable<K> keysToTest) {
    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));