[Spivak]

This is easy when you own all the code, it's a god damn nightmare the moment you introduce code that isn't yours like Redis, Postgres, Elasticsearch, every cloud API.

If you're assuming that the hundreds of millions of lines of other people's code totally outside your control always follows its spec, doesn't have bugs, or can change out from under you with no version bump (yay cloud) you're gonna be bit hard and then have to invest in integration tests.

[neurotrace]

Good point. I have always run integration tests with Postgres etc. and have found value in it. I do think that you should have a substantially smaller set of those sorts of tests though.