public function testDays()
 {
     $ci = new CarbonInterval(0, 0, 0, 1);
     $this->assertInstanceOfCarbonInterval($ci);
     $this->assertCarbonInterval($ci, 0, 0, 1, 0, 0, 0);
     $ci = CarbonInterval::days(2);
     $this->assertInstanceOfCarbonInterval($ci);
     $this->assertCarbonInterval($ci, 0, 0, 2, 0, 0, 0);
     $ci = CarbonInterval::dayz(2);
     $this->assertInstanceOfCarbonInterval($ci);
     $this->assertCarbonInterval($ci, 0, 0, 2, 0, 0, 0);
     $ci = CarbonInterval::day();
     $this->assertInstanceOfCarbonInterval($ci);
     $this->assertCarbonInterval($ci, 0, 0, 1, 0, 0, 0);
     $ci = CarbonInterval::day(3);
     $this->assertInstanceOfCarbonInterval($ci);
     $this->assertCarbonInterval($ci, 0, 0, 3, 0, 0, 0);
 }