mostly professional blather

TDD as if You Meant It at London Software Craftsmanship

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Written by keithb

August 29, 2012 at 4:10 pm

Posted in TDD

TDD as if You Meant It at XP Day London 2011

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Attendees, please add your thoughts, and links to your code repo if you wish, as comments to this post.


Written by keithb

November 21, 2011 at 11:56 am

Posted in conference, Raw results, TDD


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If you like the kind of work you see here, come join me in London. We’re hiring. Apply via LinkedIn or drop me a line.

Principal consultants take responsibility for particularly challenging solutions and in demanding organisational environments. They closely interact with senior project managers, customer representatives at all levels including senior management, and guide project teams. Together with the responsible project managers, they lead technical and strategic initiatives to success, ranging from critical consulting mandates to complex delivery projects. Together with business development and business unit managers, they actively expand Zuhlke’s business and develop new opportunities. This can involve taking the leading technical role in large bids.

Lead consultants take decisions and provide advice regarding complex technical systems. They closely liaise with the software development team, the project manager, and customer representatives, often with a technical background. They ensure that sound technical decisions are made and subsequently realised in state-of-the-art solutions by the project team. They can take the leading role in technical consulting assignments within their specialisation area.

The role is based in London and the majority of the work takes place in UK but on occasion training and consulting engagements may be delivered anywhere in the world.

The competitive package includes 20 days of professional development time per year.

Written by keithb

October 3, 2011 at 5:13 pm

Posted in Uncategorized

TDD as if You Meant it at Agile Cambridge 2011

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Attendees of the session at Agile Cambridge, please add links to you code in comments to this post.

Written by keithb

September 29, 2011 at 12:04 pm

Posted in Uncategorized

Iterative, Incremental Kanban

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There’s something about Kanban which worries me. Not kanban, which is a venerable technique used to great effect by manufacturing and service organization the world over for decades, but “Kanban” as applied to software development. More specifically, the examples of Kanban boards that I see worry me.

What you do now

David Anderson gives guidance on applying Kanban to software development something like this:

  • Start with what you do now
  • Agree to pursue incremental, evolutionary change
  • Respect the current process, roles, responsibilities & titles

Which is fine. What worries me is that the published examples of Kanban that I see so often seem to come from a place where what they do now is a linear, phased, one-shot process and the current process roles, responsibilities and titles are those of separate teams organized by technical specialism with handovers between them. Of course, there are lots of development organizations which do work that way.

But there are lots that do not. I’ve spent the last ten years and more as one of the large group of people promoting the idea that linear, phased processes with teams organized by technical specialism is a wasteful, high risk, slow and error prone way to develop software. And that a better alternative is an iterative, incremental, evolutionary processes with a single cross–functional team. And that this has been known for literally as long as I’ve been alive so it shouldn’t be controversial (although it still too often is).

Best case: Kanban will be picked up by those who are still doing linear, phased etc. etc. processes and will help them move away from that. A good thing. Worst case: the plethora of Kanban examples showing phases and technology teams undoes a lot of hard work by a lot of people by making linear, phased processes respectable again. After all, Kanban is the hot new thing! (And so clearly better).

Kanban boards

Take a look at the example boards that teams using Kanban have kindly published (note: I wish every one of those teams great success and am grateful that they have chosen to publish their results).  The overwhelming theme is columns read from left to right with a sequence of names like “Analysis”, “Design”, “Review”, “Code”, “Test”, “Deploy”. Do you see a problem with this?

Taken as a diagnostic instrument there is discussion of ideas like this: if lots of items queue up in and before the the “Test” column then the testers are overloaded and the developers should rally round to help with testing. Do you see a problem with this?

There is a way of talking about /[Kk]anban/ which strongly invites the inference that each work item must pass though every column on the board exactly once in order. This discussion of kanban boards as value stream maps, while very interesting in its own right, makes very explicit that in the view of its author the reason a work item might return from a later column to an earlier one is because it is “defective” or has been “rejected”. How is one to understand iterative development in which we plan to re-work perfectly acceptable, high quality work items with such language?

Not Manufacturing

Iterative development plans to rework items. Not because they are of low quality, not because they are defective, not because they are unacceptable, but because we choose to limit the scope of them earlier so that we can get to learn something about them sooner. This is a product development approach. Kanban is mainly a manufacturing technique. Software development resembles manufacturing to a degree of approximately 0.0 so it’s a bit of a puzzle why this manufacturing technique has become quite so popular with software developers. Added to which the software industry has a catastrophically bad track record at adopting management ideas from manufacturing in an appropriate way. We in IT are perennially confused about manufacturing, product development and engineering, three related but very different kinds of activity.

An Example

So, what if “what you do now” is iterative and incremental? What if you don’t have named specialist teams? And yet you would like to obtain some of the unarguable benefits of visualising your work and limiting work in progress. What would your kanban board look like?

Here’s one possibility (click for full-size):

Iterative, Incremental kanban board

Some colleagues were working on a problem and their environment lead to some very hard WIP limits: only two development workstations, only two test environments, only one deployment channel. But they are a cross-functional team, and they want to iteratively develop features. So, the column on the far left is a queue for new features and the column on the right holds things that are done (done recently, ancient history is in the space below). The circle in between is divided into three sectors, one for each of the three things that have WIP limits. Each sector has an inner and and outer part, to allow for two different kinds of activity: feature and integration. For example, both test environments might be in use but one for integration testing of several features and one for iterative testing of one particular feature.

The sectors of the circle are unordered. Any story can be placed in, and moved to, or back to, any other sector at any time any number of times, but respecting the WIP limit.


Why can’t I find more examples like this?

I expect that some Kanban experts are going to see this and comment that they don’t mean for groups using Kanban to adopt linear, phased processes and specialized teams. And I’m sure that many of them don’t. But that’s what the examples pretty much universally show—and we know that people have a tendency to treat examples (intended to be illustrative) as if they were normative.

I’d really like to hear more stories of whole–team iterative, incremental kanban. Please point some out.

Written by keithb

September 16, 2011 at 11:59 am

Posted in kanban

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Distribution of Complexity in Hudson

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Suppose we were to take methods one by one, at random and without replacement, from the source code of Hudson 2.1.0 How would we expect the Cyclomatic Complexity of those methods to be distributed?

Here you will find some automation to discover the raw numbers, and here is a Mathematica Computable Document (get the free reader here) showing the analysis. If you have been playing along so far you might expect the distribution of complexity to follow a power law.


This evidence suggests that the Cyclomatic Complexity per method in this version of Hudson is not distributed according to a discrete power–law distribution (the hypothesis that it is, is rejected at the 5% level).

Probability of Complexity of Methods in Hudson

This chart shows the empirical probability of a given complexity in blue and that from the maximum–likelihood fitted power–law distribution in red. Solid lines show where the fitted distribution underestimates the probability of methods with a certain complexity occurring, dashed lines where it overestimates. As you can see, the fit is not great, especially in the tail.

Note that both scales are logarithmic.

Other long-tailed distributions (e.g. log-normal) can be fitted onto this data, but the hypothesis that they represent data is rejected at the 5% level.

Written by keithb

August 31, 2011 at 8:23 pm

TDD as if you Meant It

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What’s the problem with TDD?

TDD is quite a simple process. Beck Describes it here in these terms:


  1. Add a little test
  2. Run all tests and fail
  3. Make a little change
  4. Run the tests and succeed
  5. Refactor to remove duplication

This turns out to be a hard thing to do. My observation has been that the more experienced and fluent a programmer someone is the more difficult it is for them to stick to this process. What tends to happen is more like this:


  1. Think of a solution
  2. Imagine a bunch of classes and functions that you just know you’ll need to implement (1)
  3. Write some tests that assert the existence of (2)
  4. Run all tests and fail
  5. Implement a bunch of stuff
  6. Run all tests and fail
  7. Debug
  8. Run the tests and succeed
  9. Write a TODO saying to go back and refactor some stuff later.

Really good programmers can get away with this, for a bit. But even during that early period I think they are missing a trick. A couple of tricks, in fact.

Firstly, in the pseudo-TDD steps 1, 2 and 3 can take a long, long time. Tens of minutes perhaps, hours, or days even.  This is time during which  you aren’t running tests, aren’t getting feedback and aren’t learning anything. Step 7 must be assumed to take an amount of time unbounded above.

Secondly, in the Pseudo-TDD process the programmer must fall back on some technique for making design decisions and somehow getting them right exactly at the time when they know least about the problem and its solution. In TDD we have the advantages of evolutionary design: we can discover a good-enough design and then incrementally improve it. I think it is really hard for people who know themselves to be good programmers to let go of the design process in this way.

TDD as if you Meant It

I began to wonder if there was some sort of exercise that folks could do, in safe controlled conditions, whereby they could experience the odd and surprising (and delightful) things that can happen when you really do TDD, as Beck describes it, with the hope that the experience would carry over to their daily work as programmers.

This would be a pair-programming exercise, since it’s often easier to maintain a level of discipline if you know someone is watching you can provide friendly, constructive feedback.

The problem to be solved should be simple enough that decent progress can be made on it during a typical conference “workshop” session (say, 90 minutes to 3 hours) and also have an obvious solution that experienced programmers would want to jump to implementing.

In the first couple of presentations of the session I used a problem from the game of Go. This worked reasonably well but I feel I spent too long explaining the game. Some folks who have picked the exercise up have used tic-tac-toe with good results. I tried that myself at NDC 2011 and was quite pleased with the result. From now on I will use that problem.

Another description of TDD is due to Bob Martin. It goes like this:

  1. You are not allowed to write any production code unless it is to make a failing unit test pass.
  2. You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
  3. You are not allowed to write any more production code than is sufficient to pass the one failing unit test.

I took these rules as a starting point and then tried to produce stronger rules that would force the programmer (pair) to allow the design to evolve. I don’t think I’ve yet landed on the best set of rules, and people report difficulties with various part of it, but if I were going to do the workshop today these are the rules I would enforce (subject to change and refinement at any time, last  updated 3 Sept 2011):

The Rules

  1. Write exactly one new test, the smallest test you can that seems to point in the direction of a solution
  2. See it fail
  3. Make the test from (1) pass by writing the least implementation code you can in the test method. 
  4. Refactor to remove duplication, and otherwise as required to improve the design. Be strict about using these moves:
    1. you want a new method—wait until refactoring time, then… create new (non-test) methods by doing one of these, and in no other way:
      1. preferred: do Extract Method on implementation code created as per (3) to create a new method in the test class, or
      2. if you must: move implementation code as per (3) into an existing implementation method
    2. you want a new class—wait until refactoring time, then… create non-test classes to provide a destination for a Move Method and for no other reason
      1. populate implementation classes with methods by doing Move Method, and no other way

The member of the pair without their hands on the keyboard must be very strict in enforcing these rules, especially 4.1 and 4.2

After some respectable time coding, contrast and compare solutions. Consider the classes created. How many? How big? What mutable state? Consider the methods created How many? How long? Apply a few simple design metrics. How was the experience of working this way different from the usual? How could these ideas be applied in your day job?

Experiences with the Workshop

If you haven’t tried the workshop yet, and would like to, you might want to stop reading now so that you don’t lose the “a-ha!”. That is to say: spoiler alert!


This is a tough exercise for experienced programmers and doubly so experienced TDD practitioners. I observe that pairs including folks who are not full-time programmers (BA’s, testers, managers even) do much better.

I’ve come to recognise the point about 5 to 10 minutes after the start of the exercise proper where everyone quietens down and seems to be making progress. At this point I stop the exercise and ask who has (in the case of tic-tac-toe, say) created a class called something like Board with something like a 3×3 array of ints in it (or even better, of an enum with members like BLANK and X and O) and no tests for it. After a bit of cajoling it always turns out that several pairs have. Because they “know” they will “need” it. Or because without that class they “can’t write any tests”.

At this point the facilitator needs to be strong and force them to delete that code and start again. Yes, really.

It’s extraordinarily hard for some pairs to get going. Often it’s the ones who have just had their code deleted. They will just sit and stare at an empty editor window. This is the crucial learning step. If they are not allowed to write tests about the solution that doesn’t exist yet, what are they allowed to write tests about? There is only the problem. Here is where we start to see the connection between TDD, BDD (in so far as they are not identical—hint: they are identical) and DDD and eDSLs.

There is always a startling variety of solutions.

Some pairs can implement pretty much a whole tic-tac-toe game playing program without a class remotely like a Board.


At least these people have kindly written up their experiences of doing the exercise:

Those are just the ones I know about. I’d love to hear about more.

Written by keithb

August 30, 2011 at 2:31 pm

Posted in conference, TDD

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