public function testFormat() { $dtf = new DateHandler(); $iso8601DateIntervalString = $dtf->format(new \DateInterval('PT45M')); $this->assertEquals($iso8601DateIntervalString, 'PT45M'); $iso8601DateIntervalString = $dtf->format(new \DateInterval('P2YT45M')); $this->assertEquals($iso8601DateIntervalString, 'P2YT45M'); $iso8601DateIntervalString = $dtf->format(new \DateInterval('P2Y4DT6H8M16S')); $this->assertEquals($iso8601DateIntervalString, 'P2Y4DT6H8M16S'); }