Testing APIs that use the current date and time are a pain because those values are variable. In Mailman 3 I hit upon a really dumb, simple way to do this that doesn't suck.
My wife saved two important SD cards from her camera to a faulty USB disk I'd given her. The images got corrupted and she'd deleted the files from her cards. Could Open Source come to the rescue? Let's hope so because divorces are expensive!