Stories about Software


ChessTDD 34: Specflow for Pawn Movement

This episode featured a return to progress toward shippable features.  I refactored the first feature that I’d started to use the new, idiomatic Specflow approach.  This resulted in it making the most sense to have this be the feature for pawn movement and thus progress toward implementing the pawn’s movement as well as shaking out more bugs.

What I accomplish in this clip:

  • Refactored the old Specflow feature to look like the newer one.
  • Deleted a bunch of now-dead code and made the Specflow backing class a lot more concise.
  • Implemented HasMoved from the board perspective.
  • Fixed a bug in GetMovesFrom

Here are some lessons to take away:

  • I made a mistake in deleting dead code when I had a red test.  Part of the reason I got this wrong was that the IDE crashed and I sort of lost my place, but there’s a lesson here.  It’s easy to get distracted when you see dead/unused code (or something else similar) and go off on a tangent.  That’s fine, but be sure you’re green when you go off on tangents.
  • Thinking ahead about how they code you’re writing will be useful elsewhere is a double edged sword.  It’s good because it can lead to more efficiency and less future rework, but it’s also the first step along the path to gold-plating.  There’s no exact how-to I can offer for walking this line, but just being aware of it will help.
  • When things go wrong with acceptance tests, which are coarser-grained, integration tests, your next stop in figuring out the problem will generally be to move down the test pyramid and look for more details in your unit tests.  Unit tests are going to exercise the code in more granular fashion, so you should get good insights there.
  • I recommend favoring domain-specific, communicative exceptions coming out of your code rather than allowing boilerplate exceptions to be thrown to your callers.  If someone using your code gets an array index out of bounds exception or a null reference exception, they can’t be sure whether you screwed up in your code or whether they screwed up calling your code.  If you, instead, throw “BadBoardCoordinateException”, it’ll be very clear to callers of your method that you’ve anticipated what’s going on right now, and that they’re doing something wrong.
  • Deferred execution with Linq is really powerful and allows you to do some great things, but it also leads to subtle bugs.  I’ve written about this in the past, even.  Be careful and always remember to make sure you’re aware of whether or not you’re enumerating the sequence when you run into stuff like this.

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Geoff Mazeroff

I’m looking forward to watching the video. I do have a suggestion though: Can you try to keep the content to about 18-20 minutes? As a related aside, this article talks about ideal content length for a variety of media: https://blog.bufferapp.com/the-ideal-length-of-everything-online-according-to-science.

Erik Dietrich

Wow, that’s an awesome article. I read through a bit to see what advice it had about the lengths and want to go back later to look for details on methodology. Believe it or not, I try to keep the videos to 20 minutes or so, but in the last few I’ve gotten myself into quagmires that needed more time to resolve. I’m thinking maybe in the future, it’d be better to chop it off if that happens and revert the code to that point.

Geoff Mazeroff

Now that I’ve actually watched the video, I have a design question. Isn’t adding HasMoved to the Piece class violate part of SOLID? (I’m struggling to remember which part is violated if you have parent classes with functionality that only one child needs.)

Erik Dietrich

I suppose you might make the case that it runs afoul of the Interface Segregation Principle (assuming you count properties as methods). But, in the case of Piece, Rook, King and Pawn all definitely need it, and it may be useful in some context on the rest as well. The alternative (barring a major redesign) would have been to have Board get into the business of seeing if the Piece it was dealing with was a Pawn via casting/is, and for me, that’s a much worse smell.

Guy Boicey

20 minutes, 100 characters, and all that jazz and we wonder where ADD comes from. I just spent all day watching squirrel.