PeriodList empty2 = new PeriodList(); suite.addTest(new PeriodListTest(evenMonths.subtract(null), evenMonths)); suite.addTest(new PeriodListTest(empty1.subtract(empty2), empty1)); suite.addTest(new PeriodListTest(headSet.subtract(empty1), headSet)); suite.addTest(new PeriodListTest(evenMonths.subtract(empty1), evenMonths)); sum = periodList1.subtract(periodList2); suite.addTest(new PeriodListTest(sum, 2)); sum = periodList1.subtract(periodList2); suite.addTest(new PeriodListTest(sum, periodList1)); sum = periodList1.subtract(periodList2); suite.addTest(new PeriodListTest(sum, expectedResult)); sum = periodList1.subtract(periodList2); suite.addTest(new PeriodListTest(sum, expectedResult));