Monday, June 25, 2012

Applying TDD to guitar amps

[Note: This is a repost of an entry I wrote for my company blog at]

Here at Intunity we have a really big focus on quality.  Making robust software that is flexible enough to meet clients ever changing needs (in a short amount of time) is hard.  That’s why we have all those TLA‘s floating around and other Agile terms that make non Agile practitioners wonder why we’re talking about Rugby all the time.  However once good engineering principles soak in you find that you tend to start applying those principles to other areas of your life.  For myself it was applying TDD to another problem – I thought my guitar amp had broken.  Understandably that made me a really cranky product owner and I wanted it fixed yesterday!

If you don’t know how guitar amps work, there’s a few major sections.  There’s the input, the pre-amp, the effects loop, the power-amp and finally the cab (speakers).  They’re all connected in the order listed.  Like hunting for a bug in a multi layered application I could have dived in and started randomly probing (or breaking out the soldering iron), but just as in software I would have probably wasted a lot of time.  So I “wrote a test”.  I plugged in my trusty electric, tapped my line out jack (the signal is the same that is fed into the power-amp) and played something that I knew would expose the problem.

The result – it’s all good.

I didn’t take it as a failure though as I’d halved my search area all with one test and ~1 minute of time.  Now the power-amp is a dangerous section (if you’re not careful you can get electrocuted) so before I put my affairs in order, I ran another test by plugging the amp into cab and repeating the same input.  The problem remanifested itself.  Jiggling the cable around to test for (and eliminate) a dodgy cable, I found that the cable was loose in cab socket.  Opened the back of the cab and bent one of the metal contacts back so that it touched the cable better and problem was fixed – with no electrocution risk.

All up 3 tests and 10 minutes.

To be honest the story’s pretty boring (unless you’re a guitar gear nerd) but it highlights the value of TDD in that it changes how you think about problems (and solve them).  By testing you’re understanding (or defining) your system.  You’re learning about the problem domain and setting up conditions so that you can prove a problem (if you’re bug hunting) to then fix it.  It’s also pretty obvious when you’re dealing with a piece of physical equipment that will cost you money if you break it; that you might want to be careful and not rush in.  The result ironically is that by being “slower” you’re “faster” because you’re proceeding with knowledge.

One’s software (or client’s software) is the same.  By practising TDD you have less waste, faster code, better understanding and that end product that all developers crave – a working piece of software.

By applying TDD to a more physical problem it only helped me see the more of great advantage in the practise.  After all I do like saving time and money and our clients do too :D

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