Uncle Bob Martin recently wrote “Why is estimating so hard?”. Among other things, the article explains the difference between manually doing a task (in this case breaking a text into lines of a certain maximum length) and actually writing the program to do it.
The way (many) humans do this is by trial & error, as Uncle Bob says:
Why was it so hard to write down the procedure for doing something so basic and intuitive?
Answer: Because when we do it manually, we don’t follow a procedure. What we do instead it continuously evaluate the output and adjust it until it’s right.
In an earlier article (on of before 7. Oct. 2005) “The Three Laws of TDD” Uncle Bob described three rules (or laws) of TDD:
Over the years I have come to describe Test Driven Development in terms of three simple rules. They are:
- You are not allowed to write any production code unless it is to make a failing unit test pass.
- You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
- You are not allowed to write any more production code than is sufficient to pass the one failing unit test.
The similarity between these three rules and the non-procedural way used for manual tasks surprises me: Is it possible that the TDD-way of writing software works so well, because it models the way we approach manually solving problems? Thinking of it, my first reaction is this: Sure, writing code (whether test-driven or not) is the manual work of solving some problem. So far, there’s not much news here.
But then, there seems to be more to it… To me, it is fascinating to think about the ‘meta level’ of what we’re looking at: Code writing is the manual, sapient way of creating a procedure to solve some problem. It is neither automated nor do we have a process or procedure for this kind of work.
To me TDD is an aid, a technique to help me write code in a more methodical and disciplined way. It is not at all a step to make software development more mechanical or predictable.
This brings me back to the starting point of this post: Estimating. It’s hard to predict a complex system like software development, where humans do creative work on hard problems, trying to find the solutions to problems they have not solved before. This is hard (and to me fun) work.
Should it ever turn out that there’s an easy way to (reasonably) correctly estimate it, I will be very surprised.