@Test public void testMixedRangesAndElements() throws Exception {
        IntervalSet s = new IntervalSet();
        s.add(1);
        s.add('a','z');
        s.add('0','9');
        String expecting = "{1, 48..57, 97..122}";
        assertEquals(s.toString(), expecting);
    }
Public default constructor used by TestRig
tool-testsuite/test/org/antlr/v4/test/tool/TestIntervalSet.java