That one hits home. I felt like I was being so helpful when I, fresh-eyed after finishing some entry-level C language book, suggested that we should implement unit tests to the legacy software.
The product lead, to his credit, did not chew me out, but stated very reasonably, "This software is old, relatively stable, and will likely be dead or sunset in five years. It's not worth the man-hours it would take to try retrofitting unit tests onto a piece of software this old, only for the product to be killed six months after we finish writing them."
I usually ask upfront in an interview if the team writes tests and if they don't and I get the idea they don't want to I probably wouldn't work there.