How to test hard drive - diskutility reports defective drive as perfectly fine
I reccomend Disk Drill.  Their diagnostic and monitoring tools are free, but the recovery functionality (if you need it) is what you will have to purchase.

There's also a very robust set of command line (CLI) tools available as open source:  smartmontools.  This is a available as a macOS binary package so you don't need to install via brew or MacPorts.

Important:  One thing to keep in mind when diagnosing external drives is that you have two components:


the drive itself
the USB enclosure


I have had USB enclosure's fail (the USB to SATA portion) that looked like a drive failure.  The best way to get around this is to remove the drive (if you can) and use a separate USB-SATA Adapter.  What you are doing is eliminating one of the components from the diagnostic equation (the USB interface) with a "known working" component.  They are cheap (approx $10) to keep for diagnostic purposes.



That said, a drive diagnostic is not a "quick status check."  To find bad blocks you may need to do a "deep scan" because a bad block isn't reported until the drive encounters a bad block.