Lessons Of A Craftsman: Are You Test Driving, Or Just Writing Tests?

Recently I wrote the beginnings of a blackjack game in Java, and I found myself making a common error. The Java gameplay mechanic uses a state machine to manipulate the deck.

As I was implementing the state machine I found I needed a Card object, in addition to my Card3DObject which actually drew the card, a look-up table for the 3D cards, an interface for the Deck and an object representing the Deck (so I could mock it out).

When I came across the situation for an Ace I decided a needed an object responsible for computing a Total in order to handle the situation of an Ace being a 1 or 11.

Apparently an if statement would cause an irreversible hand cramp, ending my programming career.

If you’ve ever done the bowling game, and really why haven’t you, there’s more than a few ways to skin that particular cat. Ron Jefferies has done it about four thousand different ways.

Bob Martin typically teaches a simple one. While none of them are wrong, I’m partial to the Martin version because it’s a simple problem, and it deserves a simple solution.

I can give that version to a college student, and he can understand it. Furthermore in that version the tests drive the design. Let’s go back and look at my blackjack game to see what I mean.

When writing the game I decided blackjack would be a FSM. I drew a couple of diagrams, then used the Java state machine generator to make my state machine.

The problem, as I see it, is that I did this without writing a line of code. Furthermore as I was coding I was thinking two steps ahead, and making design decisions before I needed to.

I did a mini-version of the BDUF, and it’s something I see people do all the time. I was writing test first but I wasn’t always letting tests drive that design.

Frankly that’s not necessarily a bad thing, and virtually all large systems need some design as a sort of guide, but what I should have done is wait until the code forced me into the state machine, forced me into other objects, etc.

It’s not the end of the world, and in the end I may even have made the same decisions I would have anyway, but given that I didn’t let my tests drive my design I probably won’t end up with the simplest thing that could possibly work. That’s a shame.

Eric Smith, Developer Ambassador

Eric Smith is the Lead Instructor at 8th Light's Weirich Institute of Software.

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