There is no official way to do this, ideally you would do your testing on your dev server.
The way I might do this if you really did not want users to stumble across the product and as a temporary test workaround would be to add logic to the product view template to check if the sku of the product viewed is one of your test products and then do an IP ...
Default location is
and do not include the path before the filename in the CSV data.
Starting with the Magento 2.3.2 release, the path specified in the
Images File Directory concatenates for import to the images base
directory - /var/import/images. For earlier
Magento releases, you can use a different folder on the Magento