testInvariants(rangeSet);
    assertThat(rangeSet.asRanges()).contains(Range.closed(1, 6));
    assertThat(rangeSet.complement().asRanges())
        .containsExactly(Range.lessThan(1), Range.greaterThan(6))
        .inOrder();
  }

  public void testAddEmpty() {
    TreeRangeSet<Integer> rangeSet = TreeRangeSet.create();
    rangeSet.add(Range.closedOpen(3, 3));
    testInvariants(rangeSet);

/**
 * Base class for {@link RangeSet} tests.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible // TreeRangeSet
@NullUnmarked
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) {