If you make your so-called-'unit' tests too closely coupled to you don't actually work faster though, because you constantly have to refactor them to match the internal implementation.

Your testing feedback might be quicker, but quickly getting useless information (ie. your implementation changed) is just as bad as slower tests, because you need to fix the test, recompile and again before you get useful information.

Also not all 'integration tests' are slow. If you can test using SQlite in memory, instead of pointing at a PG instance that needs to be provisioned, for instance, you can get a lot of your end-to-end testing running really quickly.