> 90% of the "unit tests" that I've observed in the wild are checking for things that a modern type system would easily prevent you from doing. I'm a heavy Clo

> 90% of the "unit tests" that I've observed in the wild are checking for things that a modern type system would easily prevent you from doing. I'm a heavy Clojure user, so I often hear how static types are unnecessary and not useful, dynamic types are much more convenient and aren't you using clojur.spec anyway to make sure your data is correct? But I'm a strong static type proponent and wish a statically typed Clojure existed. The reason is exactly as you say: with dynamic types, type errors are only found at runtime, which means the only way to find them ahead of time is to exercise the code thoroughly. So you rely on unit tests to find type errors. The problem with that is, testing is labour intensive and also non-exhaustive. You have to come up with all the ways the types might become mismatched and in my personal experience, its super easy that something slips through. These kinds of bugs seem to be the biggest cause of production errors in my code and they are the exact types of errors that a static type checker would have prevented. So I don't think unit tests area good substitute for a static type system. Many people argue that the overhead of static typing makes them too slow, is too much effort and makes it harder to write code. In my personal opinion, static types make me think about my data much more deeply and helps me design better software. Yes, its slower, but its slower because it forces me to think about the problem space more. The actual extra typing (har har) necessary to add type annotations is a very small overhead. If that's really what's making you slow, then consider learning to touchtype, switching to a better keyboard layout or better physical keyboard, an IDE with better autocompletion, just learn to use the slow down to think about your code more, or use a language with type inference. Actual writing code is a small part of my day anyway, so its not been an issue for me when I use a statically typed language. A problem I have with optional type hints is that they are optional: not all code (standard library, third party libraries) will have it, so you only get a small bit of the benefits.