/**
  * Verify full image on product page(front-end) is displayed correctly
  *
  * @return string|null
  */
 protected function verifyFullImage()
 {
     // click base image to see full image
     $this->productView->clickBaseImage();
     if (!$this->productView->isFullImageVisible()) {
         return 'Full image for product ' . $this->product->getName() . ' should be visible after click on base one';
     }
     if (!$this->isImageLoaded($this->productView->getFullImageSource())) {
         return 'Full image file is corrupted or does not exist for product ' . $this->product->getName();
     }
     $this->productView->closeFullImage();
     return null;
 }