Object Mentor Blog: TDD on Three Index Cards

TDD on Three Index Cards

Tim Ottinger — Thu, 06 Mar 2008 19:39:00 +0000

I had the opportunity to talk to a fellow who missed part of a class on TDD. I told him that I could give him a 15-minute overview, and give him all the essentials of TDD on three index cards.

Yes, I know that volumes have been written about TDD and BDD, and that it’s a large topic with many many branches of application, but I didn’t have time for that. I had time for three index cards. I figure that an index card is a token, and it represents a conversation, and that one can always dig deeper later.

They looked more or less like this:

Card 1: Uncle Bob’s Three Laws (Object Mentor)

Write no production code except to pass a failing test.
Write only enough of a test to demonstrate a failure.
Write only enough production code to pass the test.

Card 2: FIRST Principles (Brett and Tim at Object Mentor)

Fast: Mind-numbingly fast, as in hundreds or thousands per second.
Isolated: The test isolates a fault clearly.
Repeatable: I can run it repeatedly and it will pass or fail the same way each time.
Self-verifying: The test is unambiguously pass-fail.
Timely: Produced in lockstep with tiny code changes.

Card 3: Flow (using the famous three-node circle diagram) – origin unknown.

Red: test fails
Green: test passes
Refactor: clean code and tests

Sure there is plenty more, but I didn’t know how I could provide significantly less. As is, I’m pretty happy with the exercise. Now I am wondering if I couldn’t produce most of the important information I wish to convey as a series of index cards. Would that be cool or what?

"TDD on Three Index Cards" by tim

Wed, 25 Jun 2008 14:53:57 +0000

Approximating in text stinks, but :


    Red ---->  Green --> Refactor
      ^                    |
      |                    v
      ---------------------

"TDD on Three Index Cards" by Mike

Wed, 25 Jun 2008 14:05:46 +0000

Just wondering what the “famous three-node circle diagram” is referring to as a google search doesn’t return any results but this article…

"TDD on Three Index Cards" by Abdullah Cetin CAVDAR

Wed, 19 Mar 2008 18:00:47 +0000

Hi Tim,

I liked them and I have one addition from “Pragmatic Programmers” that supports yours.

Good tests are A TRIP:

Automatic Thorough Repeatable Independent Professional

Thanks a lot.

"TDD on Three Index Cards" by Tim

Tue, 11 Mar 2008 20:58:48 +0000

Well, Derick, taken that way it would definitely be wrong.

But I teach more than one topic, so I need a few three-card decks - one for each topic.

"TDD on Three Index Cards" by Derick Bailey

Tue, 11 Mar 2008 09:30:59 +0000

“Now I am wondering if I couldnâ€™t produce most of the important information I wish to convey as a series of index cards”

Doesn’t this defeat the purpose? Index cards are meant to be the smallest possible representation – a way to remind yourself of the deep knowledge and understanding present in the simple statements.

If you continue adding to the index cards – adding more index cards – you’re not providing any benefit, you’re just making it difficult to find the information by having a huge stack of cards that you need to sift through.

You could probably add 2 or 3 more cards to this list, at the most, before it reaches the point of diminishing returns. Keep the list small – keep the goals high level. If someone needs to know how to achieve the goal of card x, don’t give them more cards, sit down with them and teach them the details by coding with them.

...

that’s my devil’s advocate hat, for the morning. :)

"TDD on Three Index Cards" by JJ

Fri, 07 Mar 2008 18:41:13 +0000

How well you summarize your thoughts! I picked up from those few words on your index cards!

"TDD on Three Index Cards" by Darrell Mozingo

Fri, 07 Mar 2008 09:34:32 +0000

For more index card goodness, check out Indexed.