rangeSet.remove(Range.closed(1, 3));
    testInvariants(rangeSet);
    assertThat(rangeSet.asRanges()).containsExactly(Range.openClosed(3, 6));
  }

  public void testRemovePartFromAboveUpperBound() {
    TreeRangeSet<Integer> rangeSet = TreeRangeSet.create();
    rangeSet.add(Range.closed(3, 6));
    rangeSet.remove(Range.closed(6, 9));
    testInvariants(rangeSet);