Set<Object> seenKeys = new HashSet<>();
      BitSet dups = new BitSet(); // slots that are overridden by a later duplicate key
      for (int i = size - 1; i >= 0; i--) {
        Object key = requireNonNull(localAlternatingKeysAndValues[2 * i]);
        if (!seenKeys.add(key)) {
          dups.set(i);
        }
      }
      if (dups.isEmpty()) {
        return localAlternatingKeysAndValues;
      }

    try {
      ImmutableBiMap.copyOf(map);
      fail();
    } catch (IllegalArgumentException expected) {
      assertThat(expected.getMessage()).containsMatch("1|2");
      // We don't specify which of the two dups should be reported.
    }
  }

  // TODO(b/172823566): Use mainline testToImmutableBiMap once CollectorTester is usable to java7.
  public void testToImmutableBiMap_java7_combine() {

@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public class SortedListsTest extends TestCase {
  private static final ImmutableList<Integer> LIST_WITH_DUPS =
      ImmutableList.of(1, 1, 2, 4, 4, 4, 8);

  private static final ImmutableList<Integer> LIST_WITHOUT_DUPS = ImmutableList.of(1, 2, 4, 8);

  void assertModelAgrees(
      List<Integer> list,
      Integer key,
      int answer,

      Set<K> seen = new HashSet<>();
      BitSet dups = new BitSet(); // slots that are overridden by a later duplicate key
      for (int i = size - 1; i >= 0; i--) {
        if (!seen.add(entries[i].getKey())) {
          dups.set(i);
        }
      }
      if (dups.isEmpty()) {
        return entries;
      }
      @SuppressWarnings({"rawtypes", "unchecked"})

    try {
      ImmutableBiMap.copyOf(map);
      fail();
    } catch (IllegalArgumentException expected) {
      assertThat(expected.getMessage()).containsMatch("1|2");
      // We don't specify which of the two dups should be reported.
    }
  }

  public void testToImmutableBiMap() {
    Collector<Entry<String, Integer>, ?, ImmutableBiMap<String, Integer>> collector =

@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public class SortedListsTest extends TestCase {
  private static final ImmutableList<Integer> LIST_WITH_DUPS =
      ImmutableList.of(1, 1, 2, 4, 4, 4, 8);

  private static final ImmutableList<Integer> LIST_WITHOUT_DUPS = ImmutableList.of(1, 2, 4, 8);

  void assertModelAgrees(
      List<Integer> list,
      Integer key,
      int answer,