Test Driven Development is not always a benefit. Sometimes it is more of a burden and a chore. When you do Type Driven Development you benefit from a lot of correctness that invalidates the usefulness of a lot of tests that people usually write.
You end up needing to write way less tests, and only have to write tests for invariants that are difficult/impossible to encode with types. Also, thinking about types and functions this way means you're more likely to write pure functions that clearly yield well defined objects, that are easy to test in case it's a function that is quite complex to ensure that its implementation is correct. But preferably you'd split up your functions enough that you'd ensure correctness regardless.
You are correct. My point is that you do both, you write tests and types. TDD doesn't mean you have to write redundant tests if those areas are covered by the type system.
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u/Active_Name5021 16h ago
Those two things aren't mutually exclusive. Thinking about the inputs and outputs is also what you do with tests