@isTest
public class TestVerifyDate {

        @isTest static void testWithin30Days() {
        Date d = VerifyDate.CheckDates(date.today(),date.today().addDays(20));
        System.assertEquals(date.today().addDays(20), d);
    }

        @isTest static void testMoreThan30Days() {
        Date d = VerifyDate.CheckDates(date.today(),date.today().addDays(40));
        System.assertEquals(date.newinstance(2018,12,31), d);
    }

        @isTest static void testDateInPast() {
        Date d = VerifyDate.CheckDates(date.today(),date.today().addDays(-1));
        System.assertEquals(date.newinstance(2018,12,31), d);
    }

}