I inherited a hilarious bad(ly written) legacy system. One of the first things I did was turn on every possible "throw on error, die on error, assert" in devel

I inherited a hilarious bad(ly written) legacy system. One of the first things I did was turn on every possible "throw on error, die on error, assert" in development (could't do it production as it'd just fall over constantly). The constant crashes in dev meant I rapidly fixed the low hanging fruit (undefined indexes etc) and then slowly as I cleaned an area up I'd leave the asserts in once in production since at that point what I'm asserting is "I think I fixed all the insanity but tell me straight away if my assumption was bad". Painful very painful but those areas now cause me very few if any issues.