@GwtIncompatible // TreeRangeSet
public abstract class AbstractRangeSetTest extends TestCase {
  public static void testInvariants(RangeSet<?> rangeSet) {
    testInvariantsInternal(rangeSet);
    testInvariantsInternal(rangeSet.complement());
  }

  private static <C extends Comparable<?>> void testInvariantsInternal(RangeSet<C> rangeSet) {
    assertEquals(rangeSet.asRanges().isEmpty(), rangeSet.isEmpty());