code: protected function assertAdjustmentMode(Model\AdjustmentInterface $adjustment, string $expected): void
      {
          if ($expected !== $mode = $adjustment->getMode()) {
              throw new Exception\InvalidArgumentException("Unexpected adjustment mode '$mode'.");
          }
      }
docs: Asserts that the adjustment mode is as expected.
  
  @param Model\AdjustmentInterface $adjustment
  @param string                    $expected