Recently I started a new project at work (it was nice to shake off the cruft of an old project and pick up a new one) and my team and I are pushing harder for more professional development practices, which include writing Unit Tests. The Product Owner isn't so impressed since this translates into delayed feature delivery, in the PO's opinion.
The PO (who is also my boss's boss, which provides a bit of conflict of interest IMO) is very upset about an issue that slipped through to our release product. I'm making the point that a good Unit Test suite would have caught the issue (some additional refactoring needed to deal with some inexperienced coder's architecture blunders), and the PO wasted no time in suggesting that we "figure out how to spend some quality OT on setting up unit tests then." Our schedule is already packed with feature requests and minimal time for bug fixing and other maintenance tasks required.
I'm disinclined to offer overtime for something that I've come to learn is to be included as part of the standard development process in a team of professionals. How do I communicate that Unit Test writing is a necessary part of the day-to-day responsibility of the developer? How can I help guard my team from being demotivated by having overtime demanded of them?
PS, I don't know how to tag this, I'd appreciate any help with that, too.