/**
  * @test
  */
 public function testInvalidData()
 {
     $calculator = new Checksum();
     $subject = 'HELLO WORLD';
     $checksum = $calculator->calculate($subject);
     $this->assertFalse($calculator->verify($checksum . "DUFF", $subject));
 }
 /**
  * @param DocumentFragment[] $fragments
  * @return string
  */
 protected function calculateFragmentsChecksum(array $fragments) : string
 {
     $this->sortDocumentFragments($fragments);
     return $this->checksumCalculator->calculate(json_encode($fragments));
 }