@Override
  protected SortedMap<String, Integer> makeEmptyMap() {
    return new SimpleForwardingSortedMap<>(
        new TreeMap<String, Integer>(Ordering.<String>natural().nullsFirst()));
  }

  @Override
  protected SortedMap<String, Integer> makePopulatedMap() {
    final SortedMap<String, Integer> sortedMap = makeEmptyMap();
    sortedMap.put("one", 1);
    sortedMap.put("two", 2);
    sortedMap.put("three", 3);

import com.google.common.annotations.GwtCompatible;
import java.util.SortedMap;

@GwtCompatible
@ElementTypesAreNonnullByDefault
public class FilteredSortedMapTest extends AbstractFilteredMapTest {
  @Override
  SortedMap<String, Integer> createUnfiltered() {
    return Maps.newTreeMap();
  }

  public void testFirstAndLastKeyFilteredMap() {
    SortedMap<String, Integer> unfiltered = createUnfiltered();

        .testForwarding(
            SortedMap.class,
            new Function<SortedMap, SortedMap>() {
              @Override
              public SortedMap apply(SortedMap delegate) {
                return wrap(delegate);
              }
            });
  }

  public void testEquals() {
    SortedMap<Integer, String> map1 = ImmutableSortedMap.of(1, "one");

  @Override
  protected SortedMap<String, Integer> makeEmptyMap() {
    return new SimpleForwardingSortedMap<>(
        new TreeMap<String, Integer>(Ordering.<String>natural().nullsFirst()));
  }

  @Override
  protected SortedMap<String, Integer> makePopulatedMap() {
    final SortedMap<String, Integer> sortedMap = makeEmptyMap();
    sortedMap.put("one", 1);
    sortedMap.put("two", 2);
    sortedMap.put("three", 3);

    extends ForwardingMap<K, V> implements SortedMap<K, V> {
  // TODO(lowasser): identify places where thread safety is actually lost

  /** Constructor for use by subclasses. */
  protected ForwardingSortedMap() {}

  @Override
  protected abstract SortedMap<K, V> delegate();

  @Override
  @CheckForNull
  public Comparator<? super K> comparator() {

    public K firstKey() {
      return standardFirstKey();
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return standardHeadMap(toKey);
    }

    @Override
    public K lastKey() {
      return standardLastKey();
    }

    @Override
    public SortedMap<K, V> tailMap(K fromKey) {
      return standardTailMap(fromKey);
    }
  }

        .testForwarding(
            SortedMap.class,
            new Function<SortedMap, SortedMap>() {
              @Override
              public SortedMap apply(SortedMap delegate) {
                return wrap(delegate);
              }
            });
  }

  public void testEquals() {
    SortedMap<Integer, String> map1 = ImmutableSortedMap.of(1, "one");

  @Override
  public SortedMap<K, V> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
    return headMap(toKey, false);
  }

  @Override
  public SortedMap<K, V> tailMap(@ParametricNullness K fromKey) {

        delegate.subMap(checkValid(fromKey), fromInclusive, checkValid(toKey), toInclusive));
  }

  @Override
  public SortedMap<K, V> subMap(K fromKey, K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public SortedMap<K, V> tailMap(K fromKey) {
    return tailMap(fromKey, true);
  }

  @Override
  public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {

        delegate.subMap(checkValid(fromKey), fromInclusive, checkValid(toKey), toInclusive));
  }

  @Override
  public SortedMap<K, V> subMap(K fromKey, K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public SortedMap<K, V> tailMap(K fromKey) {
    return tailMap(fromKey, true);
  }

  @Override
  public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {