import java.io.Serializable;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.function.BiPredicate;
import java.util.stream.Collector;
import java.util.stream.Stream;
import junit.framework.Test;
import junit.framework.TestCase;

    ImmutableSortedMap.Builder<String, Integer> zat =
        ImmutableSortedMap.<String, Integer>naturalOrder().put("two", 2).put("three", 3);
    ImmutableSortedMap<String, Integer> sortedMap = zis.combine(zat).build();
    assertMapEquals(sortedMap, "four", 4, "one", 1, "three", 3, "two", 2);
  }

  // TODO(b/172823566): Use mainline testToImmutableSortedMap once CollectorTester is usable.