public function comparison()
 {
     $this->assertTrue(DateUtil::compare(new Date('1977-12-14'), new Date('1980-05-28')) < 0, 'a < b') && $this->assertTrue(DateUtil::compare(new Date('1980-05-28'), new Date('1977-12-14')) > 0, 'a > b') && $this->assertTrue(DateUtil::compare(new Date('1980-05-28'), new Date('1980-05-28')) == 0, 'a == b');
 }