The error message you are receiving is generally used as a generic error message for client-side or browser errors, likely due to a browser extension or network disruption.
If this is happening each time you attempt to delete tests, then this is likely just a local issue with your web browser or connection. Can you try this in a different browser with all browser add-ons/extensions disabled (in incognito mode), and let me know if you still get the same error?
You can also review your browser’s console log and review any error messages displayed there.
Hope this helps,