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);