Do you write your unit tests before or after coding a piece of functionality? [closed]

Question

I was wondering when most people wrote their unit tests, if at all. I usually write tests after writing my initial code to make sure it works like its supposed to. I then fix what is broken.

I have been pretty successful with this method but have been wondering if maybe switching to writing the test first would be advantageous?

Answer 1

whenever possible i try to follow a pure TDD approach:

1. write the unit tests for the feature being developed; this forces me to decide on the public interface(s)
2. code the feature ASAP (as simple as possible, but not simpler)
3. correct/refactor/retest
4. additional tests if required for better coverage, exceptional paths, etc. [rare but worth consideration]
5. repeat with next feature

it is easy to get excited and start coding the feature first, but this often means that you will not think through all of the public interfaces in advance.

EDIT: note that if you write the code first, it is easy to unintentionally write the test to conform to the code, instead of the other way 'round!