I've dabbled with rust, but did quite a bit of stuff in haskell.
A lot of unit testing is verifying failure modes. What happens if they pass in null? What happens if they ask for a value i don't know about? stuff like that. Haskell (and rust) give you a lot more control over what a function is willing to accept at compile time.
You could spend your time writing a test to ensure null is handled gracefully. With rust, you have a bit more power, and you can simply ensure the function can't be called with null. It's more general than just null checking, but that's the flavor of what happens.
That's my general feeling as well. Coming from Scala transition into "dabbling" with Rust was actually quite smooth. I try to stick to functional style where possible, exhaustive pattern matching, everything wrapped in Result/Option, etc - eliminates the need of unit testing in many cases.
A lot of unit testing is verifying failure modes. What happens if they pass in null? What happens if they ask for a value i don't know about? stuff like that. Haskell (and rust) give you a lot more control over what a function is willing to accept at compile time.
You could spend your time writing a test to ensure null is handled gracefully. With rust, you have a bit more power, and you can simply ensure the function can't be called with null. It's more general than just null checking, but that's the flavor of what happens.