I've thought about this same thing before, also in the context of not contractual work, but longterm. At least 1 thing is that if something goes wrong later on

I've thought about this same thing before, also in the context of not contractual work, but longterm. At least 1 thing is that if something goes wrong later on, you can point to the tests to show that _your work_ is no the culprit. I'm curious to hear what the more experienced people have to say on your question.