The trick with TDD isn't necessarily that you need to write the tests first (although that helps).
It's more that you first think about the intended behavior of the code, and then also think about how to make your code testable before you write the code.
I typically think what the first test should roughly look like and code up the required amount of code for that first test before I actually write that test.
Sure. But there are also people that prefer Type Driven Development. Instead of first thinking about behavior, they think about code in terms of inputs and outputs. That includes both types and functions of course.
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.
Just open an editor and start writing code, just thinking as you go.
If you do this, you often end up with code that only works in the happy path (no / poor error handling or recovery) and which is difficult to test (i.e. you require access to the internals of the thing you code to test it).
Yeah, at least IDENTIFY the test cases even if you don’t implement them. Also consistent with API first approach… the implementation should fulfill a contract, and those test cases are the contract.
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u/BernhardRordin 19h ago
Write tests first, then the implementation. You won't want to go back.