> I genuinely don't get how you can rely primarily on unit tests to prevent regressions in your code. They are at such a fine granularity that most significant

> I genuinely don't get how you can rely primarily on unit tests to prevent regressions in your code. They are at such a fine granularity that most significant changes require restructuring the "units" in a way that invalidates the tests. Besides less-anemic E2E tests, this is why type systems exist. Define a well-typed interface, code to the interface, test the units — and then it's hard to make terrible mistakes wiring things up. To realize the full benefit does, of course, require substantially better data structures than string-to-Any hashes, and it requires some proper old-school software engineering (i.e. injecting a client as an argument and not just mocking out the someOtherClient.client() method.) And there is some overhead, though I'd say that a proper null-checking pass alone would be worth that much. (Sorry, Java, your types are terrible.)