Study on benefits of TDD

OK, this isn’t news, this study came out a couple of years ago and was covered by many people then. But, I find myself regularly referring to it trying to find the link. So I’m going to blog about it then I’ll always be able to find the link.

The study is by Nagappan, Maximilien, Bhat and Williams and is entitled: Realizing quality improvement through test driven

development: results and experiences of four industrial

teams and is freely downloadable from Microsoft.

This is the key findings are summarised in this table:

Team /


IBM drivers

Microsoft Windows


MS Visual Studio

Defect density of comparable team not using TDD





Defect density of team using TDD





Increase in time taken because of TDD





The way to read this is: the researches looked at two Microsoft MSN teams, one team did not use TDD and had a defect density of Y. The second MSN team had a defect density less than a quarter of Y but took 15% longer.

To my mind that proves that which was to be proven, i.e. TDD reduced bugs. But, I’m also aware that other writers have disputed this and I’ve heard of studies which disprove it. (Anyone got a link? Thanks)

Most people who I’ve met, and who have practices, or understand TDD agree it is effective. However there are those who don’t believe it. It reminds me of the episode of Black Adder where Rowan Atkinson’s Black Adder hires a ship Captained by Tom Baker. When there is a problem it plays out like this:

Black Adder: “Someone in the crew will know… you do have a crew don’t you?”

Captain: “Arh, opinion is divided on the subject… all the other captains say you need a crew, and I say You Don’t”

At the end of the day Confirmation Bias will probably decide which set of results you choose to believe.

Ed Yourdon on Agile

Ed Yourdon seems to have fallen off my radar so far this century. Last century I read a lot of his stuff and came to respect him as a man who knows what he’s talking about when it comes to IT and software development.

(If you haven’t heard of him, or don’t believe me just look at the list of books he’s written.)

I recently discovered that he has a blog, and from there that he has recently been to the Agile 2010 conference. In fact it appears that the whole Agile thing has, to a large part, passed him by.

The really interesting thing are some of his comments on Agile from this blog posting:

  • ‘My overall impression is that “agile” (and its variations, such as scrum and XP) are now entering the “mainstream” of computer systems development’
  • ‘there’s still a lot of hype and exaggeration, along with a non-trivial amount of myth and folklore and general silliness. But when you strip away all of this, there is a very solid, and extremely well-documented, core of practical system development guidelines, concepts, strategies, and hard-won lessons that every practitioner in our field needs to know about.’

I’m happy to find myself agreeing with Ed, and even happier that the voice more experience sees it the same way I do!

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The No Business Case Myth

Once in a while I run across individuals, or even teams, who still think Agile is about just getting on and doing it. Well it is, good for them, but, that doesn’t mean there isn’t a reason for doing it.

There seems to be a myth in some circles that work done using Agile techniques doesn’t require a business case. Lets get this clear: Agile does not excuse you from having a business case for your work.

Of course there are instances were a business case might not exist. Some companies, for better or worse, work without them; those companies aiming at innovation may allow work to proceed to a more advanced stage before asking for some rationale; and products which are in a steady state may just tick over without too much attention to a business case.

But in each one of these cases the lack of a business case has nothing to do with Agile. (Actually, each of the cases does have a business case, its either a tacit business case or a part of a much bigger business case.)

Many development efforts which lack a visible business case can benefit from demanding a business case. If you are not sure why your company is doing some piece of work then maybe the company needs to be clearer about the reasoning.

However, a business case might look a little different on a Agile project. It may well be shorter than a traditional business case, it may lack some of the detail traditionally found in a business case, and it may describe much more a trial-and-error approach.

What Agile projects don’t need are in-depth business plans. Here its a question of detail, a strategic business plan makes plenty of sense. But a business plan which lists many many features to be build and a detailed schedule of when they will be built is little more than an illusion. Such plans give the appearance of certainty but certainly don’t provide it. Indeed, too many plans can actively hinder a project – plans are not benign, they are dangerous. (See An alternative view of design (and planning) for more discussion here.)

That said, there is a very good case for writing a business plan – indeed most forms of plans actually: they are rehearsal time for the real thing. They help you explore and learn about the thing you want to build.

Still, sometime you might skip the business plan. Maybe there isn’t time for a rehearsal, and sometimes learning can be maximised but just getting stuck in .

But, if you do write one, then once that exercise is over, once you start doing it for real, don’t try and hold yourself to a plan. Put the plan in the draw and don’t look at it. The value of planning is not the plan you produce at the end of planning; the value it is the knowledge you acquire in your head.

For that reason you want to maximise the number of people involved in the planning rehearsal so you can maximise the learning.

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I'm a BA get me out of here! – the BA role on an Agile Team

In the last couple of years I’ve given my “BA role in Agile” (PDF of the Nottingham version, or Slideshare of the Skills Matter version) talk a number of times at a number of different venues. A couple of months ago I got around to writing up the talk and it has now been published in ACCU Overload.

If you’d like to read this you can read it in Overload 98, or take the PDF from my website, “The BA role on Agile teams”.

Shorter versions of this piece have, and probably will be again, published elsewhere. The Overload piece is the full version. Thats the nice thing about Overload, it has the space to explore a topic more fully.

I’m just now putting the finishing touches to the 3-day training course that grew out of this talk and which will be running in September at Skills Matter.

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Conferences, Conferences, Training – a busy autumn


I’m speaking at a bunch of conferences this autumn so if any reader out there would like to hear me speak, or ask a questions you might get yourself a ticket to one of these:

In between times, I’m also delivering several public training courses – not to mention private ones but there is no point in me telling you about those.

What’s particularly interesting here is the new “Agile for BAs” courses that I’ve put together with Chris Matts. The first of these ran last week in association with BA Solutions and was well received. A different, longer, version of this, is running in association with Skills Matter twice this autumn:

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