Special File that causes I/O error

I want to automatically test if a piece of software reacts as expected if an essential SQLite DB file fails to be read (causing an I/O error). Exactly that happened some days ago at a client. We manually fixed it but now I want to create automatic code to fix it and need access to a broken file to test that.

Show different theme for admin?

I’d like to test some theme changes on my live site, but I obviously don’t want regular users seeing any errors that may arise from it. I’d like to just duplicate my theme folder and if I’m logged in as admin, then that theme is shown to me, otherwise, the old theme is shown to my users.