@Test public void testMergeWithDoubleOverlap() throws Exception {
		IntervalSet s = IntervalSet.of(1,10);
		s.add(20,30);
		s.add(5,25); // overlaps two!
		String expecting = "{1..30}";
		String result = s.toString();
		assertEquals(expecting, result);
	}
This case is responsible for antlr/antlr4#153.
https://github.com/antlr/antlr4/issues/153
tool-testsuite/test/org/antlr/v4/test/tool/TestIntervalSet.java