public void testFloor() {
    resetWithHole();
    assertEquals(a, navigableMap.floorEntry(a.getKey()));
    assertEquals(a.getKey(), navigableMap.floorKey(a.getKey()));
    assertEquals(a, navigableMap.floorEntry(b.getKey()));
    assertEquals(a.getKey(), navigableMap.floorKey(b.getKey()));
    assertEquals(c, navigableMap.floorEntry(c.getKey()));
    assertEquals(c.getKey(), navigableMap.floorKey(c.getKey()));
  }

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

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

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

  }

  @Override
  @CheckForNull
  public Entry<Range<K>, V> getEntry(K key) {
    Entry<Cut<K>, RangeMapEntry<K, V>> mapEntry =
        entriesByLowerBound.floorEntry(Cut.belowValue(key));
    if (mapEntry != null && mapEntry.getValue().contains(key)) {
      return mapEntry.getValue();
    } else {
      return null;
    }
  }

  @Override

  }

  @Override
  @CheckForNull
  public Entry<Range<K>, V> getEntry(K key) {
    Entry<Cut<K>, RangeMapEntry<K, V>> mapEntry =
        entriesByLowerBound.floorEntry(Cut.belowValue(key));
    if (mapEntry != null && mapEntry.getValue().contains(key)) {
      return mapEntry.getValue();
    } else {
      return null;
    }
  }

  @Override

    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));

    public Entry<K, V2> firstEntry() {
      return transformEntry(fromMap().firstEntry());
    }

    @Override
    @CheckForNull
    public Entry<K, V2> floorEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().floorEntry(key));
    }

    @Override
    @CheckForNull
    public K floorKey(@ParametricNullness K key) {
      return fromMap().floorKey(key);
    }

    public Entry<K, V2> firstEntry() {
      return transformEntry(fromMap().firstEntry());
    }

    @Override
    @CheckForNull
    public Entry<K, V2> floorEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().floorEntry(key));
    }

    @Override
    @CheckForNull
    public K floorKey(@ParametricNullness K key) {
      return fromMap().floorKey(key);
    }

    return keyOrNull(lowerEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> floorEntry(K key) {
    return headMap(key, true).lastEntry();
  }

  @Override
  @CheckForNull
  public K floorKey(K key) {
    return keyOrNull(floorEntry(key));
  }

  @Override
  @CheckForNull
  public Entry<K, V> ceilingEntry(K key) {

        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    @CheckForNull
    public K floorKey(K key) {
      synchronized (mutex) {

        return nullableSynchronizedEntry(delegate().firstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> floorEntry(K key) {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().floorEntry(key), mutex);
      }
    }

    @Override
    @CheckForNull
    public K floorKey(K key) {
      synchronized (mutex) {