With strong, expressive type systems such as those offered by Haskell, Rust, TypeScript, etc... I find that you front-load all of your debugging to compile/typecheck time. Instead of needing to experiment with your code at runtime through either manual or automated (TDD) tests, you are instead having a conversation with the compiler/typechecker to statically guarantee its correctness. There's just as tight a feedback loop with a typechecker as there is with a test runner; you in fact get your feedback even sooner during compile time, instead of during the subsequent runtime.
Where static verification against a typechecker shines over runtime verification against a test suite is that a test suite can only demonstrate the presence of bugs; type systems demonstrate their absence (presuming of course that you understand how to encode certain invariants into your types and don't do some foolishness such as simply asserting all values as `any`).
Where static verification against a typechecker shines over runtime verification against a test suite is that a test suite can only demonstrate the presence of bugs; type systems demonstrate their absence (presuming of course that you understand how to encode certain invariants into your types and don't do some foolishness such as simply asserting all values as `any`).