I'm sure the TDD book is getting fat now, but I'd like to read a dialog like
this in there somewhere...

I'm massively editing what Robert (r.blum@...) and someone else, someone
named Kent(?) wrote... Since I'm changing the text, I'll use different
names.

Calvin: "I don't do test driven programming. I write some code, and test it
manually, walking through it in the debugger, checking that it works."

Hobbes: "How do you know that it works? Could you express that as a test
before you run your code?"

Calvin: "I can't think about the test until I've thought about the code"

Hobbes: "Changing the habit of writing code before the test can be a bother.
Try this: Write the code on paper. Then write a test."

Calvin: "Paper?!"

Hobbes: "What if you just outlined the code on a whiteboard and didn't write
any real code? Could you still write a test first?"

Calvin: "I'd feel silly doing that alone."

Hobbes: "What if you explained it to your pair partner? Could you still
write a test first, or maybe have your pair partner write the test?

Calvin: "That could work."

Hobbes: "I notice you're refactoring without tests. What's that like?"

Calvin: "After I refactor, I have to test it again manually, in case I make
a mistake doing the refactoring."

Hobbes: "Wouldn't it be easier to run some quick tests before and after you
you refactor?"

Calvin: "Well duh! If I had the tests."

Hobbes: "If you do test-driven development, your tests drive the design of
your code, and as a side-benefit, you get a nice small set of regression
tests that make refactoring safe."

Calvin: "Perhaps if I start by thinking about the interfaces that my class
or module would need to support, I would be able to write the unit test
first? Does this sound like the kind of thing I should be trying more of?"

Hobbes: "I think so. If I were given just the task of writing a class or
module, my first test would describe a very simple case of what I wanted
from that code. The interface of this not-yet-written code is evolving, of
course, during my test-driven development process. Since I'm calling the
functions that I need at each moment, without a care how (or if) they are
implemented, it tends to create a pretty useable interface."

Calvin: "So you find out quickly if your interface functions are no good
when you're forced to use them as client, in the tests, before investing a
lot of work at writing them!"

Hobbes: "Now you're getting it."

Calvin: "Tell me, when you think of a feature, is your next thought about
testing or implementation?"

Hobbes: "I just think about using that feature. Which leads me to an example
of how I would use it. Now I just write down the results I expect from that,
and voila, there's the test. I'm not even actively thinking 'I have to write
a test now. How can I test it?'. My main focus is how I can use it."


----

C. Keith Ray
<http://homepage.mac.com/keithray/resume2.html>
<http://homepage.mac.com/keithray/xpminifaq.html>