I think it should be a standard to have hardware come with a full suite of tests that can be accessed by anyone, without any kind of login. Otherwise, repair shops will keep asking for full access.

In my case, many years ago, I got asked by a phone repair shop to backup the phone and wipe it before handing it over unlocked. My understanding was, they had no good way of doing proper diagnosis and after-repair testing without full access to the system.

Like a password enabled BIOS option to allow for booting off of external storage with no access to onboard storage provided? “Valet mode” if you will.

Valet mode! Excellent.

Macs have an "Apple hardware test" you can boot into. And you could as well just boot from an external drive to run all kinds of diagnostics.

Phones however...

There is a diagnostic tool for iPhones/iPads, too. It's just not accessible to the general public.

https://www.ifixit.com/News/33593/heres-the-secret-repair-to...

Androids usually have some magic buttons to get into a bootloader prompt; you could have a diagnostic in there, perhaps.

You can boot into fastboot (a barebones flashing and unlocking mode implemented by the bootloader itself) and recovery (a real kernel + minimal UI on top to apply updates and wipe). From fastboot mode, you can boot into an arbitrary image, but that obviously requires an unlocked bootloader. Unlocking the bootloader almost always performs a wipe "to protect data".

In principle, it should be possible to have a diagnostic mode the same way recovery is implemented. But there are no device I know of that have this.

I see what you mean, but that sounds like a gigantic attack surface for all the companies that sell oppressive regimes tools for hacking into arrested human rights activists' phones.

It depends on how it's designed. It wouldn't be that expensive to add a second memory chip. Provide some way to boot to the alternate, when the alternate is running the primary isn't even powered up. Zero attack surface.

> If the repair is finished and the tech can get to the login/pin screen then the job is done.

Not entirely https://www.macrumors.com/2018/09/17/iphone-calibration-proc...

It is actually sometimes necessary to do some calibration and system tests, I don't know the details but it's basically because Apple wants to screw over third-party repair shops.