}
    ImmutableMap<ClassWithTerribleHashCode, Integer> map = builder.buildKeepingLast();
    assertThat(map).containsExactlyEntriesIn(expected).inOrder();
    assertThat(map).isInstanceOf(JdkBackedImmutableMap.class);
  }

  @GwtIncompatible // Pattern, Matcher
  public void testBuilder_keepingLast_thenOrThrow() {
    ImmutableMap.Builder<String, Integer> builder =
        new Builder<String, Integer>()

    } catch (BucketOverflowException e) {
      // probable hash flooding attack, fall back to j.u.HM based implementation and use its
      // implementation of hash flooding protection
      return JdkBackedImmutableMap.create(n, entryArray, throwIfDuplicateKeys);
    }
  }

  private static <K, V> ImmutableMap<K, V> fromEntryArrayCheckingBucketOverflow(

          Entry<K, V> onlyEntry = requireNonNull(entries[0]);
          return of(onlyEntry.getKey(), onlyEntry.getValue());
        default:
          entriesUsed = true;
          return JdkBackedImmutableMap.create(size, entries, /* throwIfDuplicateKeys= */ true);
      }
    }

    /**
     * Scans the first {@code size} elements of {@code entries} looking for duplicate keys. If