@Test public void testMergeWhereAdditionMergesThreeExistingIntervals() throws Exception {
		IntervalSet s = new IntervalSet();
		s.add(0);
		s.add(3);
		s.add(5);
		s.add(0, 7);
		String expecting = "{0..7}";
		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