Documentation? You mean tests?

"I hate writing documentation!"

I've seen more than a few programmers say this.  To be honest, I've been guilty of saying it occasionally.  This post isn't about convincing you to like writing documentation.  I already wrote that post.  This post is about something I was talking to a coworker about just the other day.

Tests are documentation

I don't just mean that like when other programmers say it.  "Tests are one form of documentation."  This is much bigger than that.  When you test correctly and thoroughly, it's better than documentation.  That's when sh*t gets real.  I talked a bit about testing before, but what I said was only a piece of the whole.  Tests are the best form of documentation there is.  When you test code you don't understand, the test is a window into what you were thinking at the time.  It shows how the code works when it's done, but only by showing how you figured it out.  How many times have you looked at a piece of code and thought "What was he/she thinking when he/she wrote this?"  That's exactly what a test clarifies.

I'm not talking about TDD, but I am talking about testing.  I have yet to effectively use TDD.  It feels like predicting the future.  I don't know what I'll need to write before I write it, so I write it, then test it.  But I do test it.  I write End to End Tests, Unit Tests, and Acceptance Tests.  And, I demand nearly 100% code coverage.  I don't test generated code, but all of my code is tested, and well tested at that, I'm talking about testing by passing null parameters, and even with junk data.  I judge the quality of a Solution based on the size of the testing Project. Why?  Because if I ever don't know how something works, I can just run the tests for it and know everything about it.  (In fact, I'd love to see VS add to the context menu "Run Tests that Include this Method")

Tests are better than other technical documentation forms

While automated testing is useless at making end user documentation, this form of documentation is more detailed than standard technical docs, and on top of that it changes as the code changes, so it's always up to date.  More than that, it also gets checked into source control, so you can see the historical documentation side-by-side with the historical code.  This form of documentation grows with your code, it is "living" documentaiton.  More than anything else, it's ACCURATE.  There's not a 10 year old piece of paper suggesting that Server XYZ currently hosts the database for this project.  It's all there and you can see proof that this is how things work.  It's beyond documentation.  It's amazing when done properly.

It's not going to happen overnight

Do not imagine this is some magic wand that you can wave.  I'm working on a 3 week contract that I opened up a Solution with 0 tests on my first day.  While building code for the project I've only had time to write about 3 tests (by the end of week 2).  This is something you should implement on any new projects and work to implement over time on old projects.  But as a result, you'll never have to be afraid of making a change again.  Can you imagine that?  I know I would love to be in that position.