@Test
    public void testOccurs() {
        System.out.println("occurs");
        for (int year = 1900; year < 2010; year++) {
            for (int month = 0; month < 12; month++) {
                GregorianMonthly instance = this._first;
                boolean expResult = true;
                boolean result = instance.occurs(year, month);
                assertEquals(expResult, result);

                instance = this._ninth;
                result = instance.occurs(year, month);
                assertEquals(expResult, result);

                instance = this._thirtyFirst;
                expResult = true;
                switch (month) {
                    case 1:
                    case 3:
                    case 5:
                    case 8:
                    case 10:
                        expResult = false;
                        break;
                    default:
                        expResult = true;
                        break;
                }
                result = instance.occurs(year, month);
                assertEquals(expResult, result);
            }
        }
    }