> The bar is far lower in test cases (where I usually use File::Slurp) than in production (where I don't)

I feel this is a dangerous mindset, especially in larger organisations, as indicated by these two points from Effective Automated Testing:

• Automated test suite needs ongoing maintenance. So test code should be well-designed and maintainable; that is, you should avoid the common pitfall of "oh, it's only test code, so I'll just quickly cut n paste this code".
• It's vital to quarantine intermittently failing tests quickly and to fix them quickly ... only returning them to the main build when reliable (if you don't do that, people start ignoring test failures!). No broken windows.

👁️🍾👍🦟