Also recently did Thorsten Ball's Interpreter/Compiler books which focus heavily on unit testing the functionality (I can't recommend these books enough).
I now can't imagine going back to a pre-TDD world
However at work, I often find that I feel like I can't write unit tests before starting code because I just don't know how it's going to get built until I start poking at the code. I'm not sure how to break out of this
You'd start with shallow functions and quality asserts. Initially, you'd have broken tests, you have to write code to fix them, and that's your TDD.
Your comment is exactly what I try to get across in the book but it's not always easy.
If you cant decide how you want something to look (as that's not always easy) just take a punt on something. Make sure it's a small decision and make something useful. Sure you might have to change it, but at least you'll be basing that on some real feedback.
One thing I was uncomfortable with about TDD is the step to "just write enough to make the test pass". The danger seems to be when you have to walk away from some code and you or whoever picks up your code doesn't know what you were up to.
In a simple app and a few tests you could probably tell, but the larger an application gets, the less you can put effort into finding out "this test works because the application works how it should" or "this test works because someone wrote just enough code and hardcoded some value somewhere in order to make the test pass".
It seems "safer" to write tests that are going to stay broken until every little corner of everything works properly, even though this is less iterative.
As mentioned above I have little TDD experience, so maybe I'm missing something.
This is the _only_ point where you can safely refactor, if your tests are failing how do you know you haven't broken something? So long as you keep things "green" you know you're ok
> The danger seems to be when you have to walk away from some code and you or whoever picks up your code doesn't know what you were up to.
Just don't do this. You're not "done" with the TDD cycle until you make it pass and have refactored.
I reflect this in my git usage too, roughly it goes
- Write a test -> Make it pass -> git commit -am "made it do something" -> refactor -> run tests (if i get in a mess, revert back to safety and try again) -> git add . -> git commit --amend --no-edit
> It seems "safer" to write tests that are going to stay broken until every little corner of everything works properly, even though this is less iterative.
The problem with this is how do you safely refactor when you have potentially dozens of tests failing?
A big point of this approach is it makes refactoring a continuous process and makes it easier because you have tests proving you haven't accidentally changed behaviour.
Once the code compiles I go into the implementation and make it work.
Now and then I realize during implementation that I need some additional parameter, but it's easy to add that.
1) Writing a test that calls an API and asserts that everything resulted correctly from it is more of an integration test in my opinion - in this case I can agree this can be written beforehand.
2. If I'm changing my tests as I write my code then it doesn't matter if I go test-code-test-code vs code-test-code-test. I have still changed my definition of "correct" on the fly based on something I found out as I implemented.
That is, you don't need to test that inbuilt standard library stuff is working as expected (e.g does a string reverse) but rather, does the combination of possible inputs match your expectations?