Category Archives: software

Teaching TDD from the ground up

One of the first steps in any embedded software project is to implement an assert macro.  This is true for a few reasons:

  • you have certain assumptions about how the hardware should behave and you want to know when those assumptions are broken,
  • you need a way to signal outside of the custom hardware when something has gone wrong,
  • there is no standard function that can deal with these problems.

This might seem like a wasteful thing for every project to undertake, but actually it is a very constructive place to start.  Firstly, it frames the development around verification.  Secondly, when you find a bug you don’t start printf debugging, instead focusing on adding assertions.  And finally, from the very outset of the project you demystify the black box of your embedded system.

In the same way, I think that the first step in learning test driven development should be to write a testing framework.  And it needn’t be difficult – a simple test framework can be written in a few lines of code.  This is the test framework for testing the fake function framework.

/* Test Framework :-) */
void setup();
#define TEST_F(SUITE, NAME) void NAME()
#define RUN_TEST(SUITE, TESTNAME) printf(" Running %s.%s: \n", #SUITE, #TESTNAME); setup(); TESTNAME(); printf(" SUCCESS\n");
#define ASSERT_EQ(A, B) assert((A) == (B))
#define ASSERT_TRUE(A) assert((A))

It could be even more concise, but I wanted to make it compatible with the googletest framework so I can re-use the test cases in both C and C++ without modification.  Anyway, you get the point.

I am a big fan of testing frameworks, and for sure there is no need to re-write junit every time we start a new java program.  But for learning TDD, I think a lot of the mystery would disappear when participants make a simple test framework and use that to make their first few tests.



Filed under fff, software, testing

Hierarchy of Software Needs

What happens when I apply Maslow’s hierarchy of needs to software?
Maslow's Hierarchy of Needs


  • Breathing: There is a user for this software.
  • Sex: It compiles.  Software that does not compile has no future.


  • Morality: It adds value.  Software that does not add value does not survive.
  • Security of body: The software is under version control.
  • Security of health: There are no compiler or static analysis warnings.
  • Security of resources: There are limited signs of broken windows.  Tests, if any, run successfully.  Commented out code is minimal.


  • Friendship: The software meets the needs and expectations of the users
  • Family: Developers enjoy working on the software


  • Achievement: Developers are proud of the software
  • Confidence: tests and quality assurance mean making changes is a low risk proposition.
  • Respect of others: Future developers needs are considered
  • Respect by others: Users and stakeholders trust in the software to meet their needs.


  • Morality: The code is “Good”.
  • Acceptance of facts: The software has executable Acceptance Tests to define it’s requirements.
  • Lack of prejudice: The problem domain is perfectly expressed in the source
  • Creativity, Spontaneity: It is easy and cheap to experiment with the code.
  • Homoiconic?

This may be a flawed extension of a flawed model, but the central point is that before the basic physiological and safety needs of the software are meet it is really difficult to focus on the higher motivations of software development.  This might also provide some clues as to where to start cleaning house on legacy renovation project.

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Filed under legacy, quality, software, Uncategorized

Fake Function Framework – Request For Comments!

I have a little micro-framework called fff.h for generating fake functions (mocks) in C.  I have blogged about it in the past, and there have been some exciting changes over the last few weeks that I’d like to share.


The basic premise is that testing a C source file is difficult in idiomatic C because of all the external function calls that are hardwired into the production code.  The way fff.h helps is to make it a one-liner to create fake implementations of these for the purposes of testing.

Now, the basic formula on my last project for testing a C module is like this:

Typical approach to testing legacy C code

This was crude but effective.  What really grated with me though was the amount of repetitive code that had to be written to answer very basic questions.  Was my fake function called? How many times? What parameters were passed in on each occasion? Was the unlock function called before the write function? To answer these questions we ended up writing endless amount of (not very pretty) code like this:

Manual Fake Functions

It seemed to me that it should be possible to write a macro to generate this code.  This would tidy up the test files in terms of readability and would make it easier for my team to make tests.  And that was the genesis of the Fake Function Framework.

The best introduction to the Fake Function Framework is on the fff github site so I won’t rehash that here.

New Developments

I have since moved on to a new project and haven’t thought about fff.h in a wee while.  Through a variety of coincidences it happened that Tore, the architect on my previous project, met James Grenning during a training course and introduced him to fff.h. James played around with fff.h and sent me some great suggestions for cleanup, and how to improve fff.h to produce globally linkable fakes.  At first I thought that this was an unneeded complication for an otherwise simple framework, but James convinced me that reusable fakes had a lot of value.

I set to work on making the generator able to generate the new style fakes.  I don’t know I would have attempted this without having a full regression test suite for the framework.

The way it works is instead of using the usual syntax to create a fake using the FAKE_xxx_FUNCn macros, you create a header file to hold the declarations:

Global Fake example header file

Global Fake example header file

And then create an implementation file for the function definitions:

Global Fake implementation file example

Global Fake implementation file example

Then you can link many test suites against this single object without any problems. Simple!

Breaking Changes

There have been some breaking changes to fff.h to enable these new features, and I have also taken that opportunity to clean up some weaknesses in the previous design.  But since fff.h is just a header file, both will happily exist in your codebase. All you have to do is name the new version of fff.h fff2.h and start using fff2.h in your new tests.

So theses are the basic changes you should know about if you are already familiar with the fake function framework.  Somewhere in the test executable you must define the globals for fff.  Why not put it beside the main function?

Define FFF globals

In the old version of fff.h there was a shortcut for resetting all the fakes in one step.  This is now gone. The reason is that it only worked in C++ using static initializers and the introduction of global fakes were incompatible with this.

Reset Fakes

There has also been some cleanup.  All the fake function framework variables have been moved into a struct to avoid polluting the global namespace.

fff globals now in struct

fff globals now in struct

And the variables for individual fakes are now defined in a struct.

Fake function data now in struct


The fake function framework would not exist as it does today without the support of key folks.  Tore Martin Hagen (and his whiteboard), my partner-in-crime in Oslo, was instrumental during the genesis of fff.  Jon Jagger, who during ACCU 2011 helped me teach the preprocessor to count.  And James Grenning, who convinced me the value of global fakes, sent me a prototype Implementation, and showed me how expressive a DSL can be.  Thanks to you all!

Request for comments

I hope you like the new changes, and if you have any feedback or suggestions for further improvements don’t hesitate to leave a comment or contact me via twitter.

Further reading


Filed under fff, quality, software, testing

Metricide (or The Curious Consequences of Counting)

This is a PowerPointPoem I gave at the ACCU 2012 conference


Filed under quality, software

Retrospective – Global Day of Coderetreat, Beijing!

On the 3rd of December a small collection of developers gathered in a basement conference room in Beijing to practice the craft of software development. The participants came from diverse backgrounds: architects, developers, students, and managers. There were people comfortable with C++, C#, Java, Python and others hadn’t programmed in a couple of years. Here are my notes from the day:


Coderetreat is a day-long, intensive practice event, focusing on the fundamentals of software development and design. By providing developers the opportunity to take part in focused practice, away from the pressures of ‘getting things done’, the coderetreat format has proven itself to be a highly effective means of skill improvement. Practicing the basic principles of modular and object-oriented design, developers can improve their ability to write code that minimizes the cost of change over time.

A coderetreat is a language-agnostic event. In each session, the pair chooses what language they want to work in. The day focuses on practicing the fundamentals of software: TDD and the 4 rules of simple design; these are applicable regardless of language.

Alex and Zilong pairing

Chocs Away!

After a brief introduction, we went into the first session to familiarize ourselves with the task: Conway’s Game of Life. Participants struggled with deleting the code at the end of the session; this was one of the biggest challenges that they faced throughout the day. The second session was to swap pairs and have a second go at the problem with a clean slate. The third session introduced the concept of ping-pong TDD.

Gospers Glider Gun

For lunch we went out to a local restaurant to get a chance to stretch our legs and have a fresh perspective.



In the afternoon we tried a couple of CyberDojos. The first session we didn’t change pairs so we could have a chance to get familiar with the CyberDojo software. After a few technical issues we were on our way. In the second session we changed the pairs every five minutes, really challenging ourselves to write code in very small increments.



The final session I gave the participants a choice: we could agree as a group to either try to create the absolute best code we could for the solution, or we could try to create the absolute worst code possible that implements the solution. It was a tough call but the dirty code challenge won out. In this session there were many creative approaches and a notable visual implementation that looked great in the UI and was a hornets nest in the implementation – you know who you are! ☺

At the end of the day we held the usual Closing Circle, where we each share with the group our feelings on what went well, what was surprising, and what we can take away from the event. There was a general consensus that the day was fun and that it highlighted the importance of communication, both between people and through the code. Also surprising was how many different approaches there were to the same problem.


Hello from Japan!

Hello from Japan!

The event is called a “Global Day” for a reason; the same event was happening in over 90 cities across the world on the same day. There were many ways the events connected, lots of activity on twitter with the hashtag #gdcr11, and several events talked to each other via google hangouts or skype. We had a quick chat with the coderetreat in Tokyo in the morning, and before lunch we managed a chat with the folks in Perth, Australia. This was a lot of fun and helped to energise the group.

Hello from Perth!

Hello from Perth!

Thanks to Corey Haines and Jim Hurne for organizing the global day, and also thanks everyone that helped me organize in Beijing. Thanks to Tokyo and thanks to Perth. And special thanks to everyone in Beijing who came along on a blue sky day to spend their Saturday in a basement coding with other software craftspeople.

p.s. I am starting a local software craftsmanship meetup group here in Beijing, sign up to hear about future events and meetings!

Related Posts:
Interview with Corey Haines

Tags: software testing craftsmanship coderetreat coreyhaines tdd

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Filed under coderetreat, software, testing

Improve your codebase with a Code Dugnad

In an ideal world the codebase you work on is a pristine oasis of pure logic, a magnificent expression of the problem domain, a testament to power of rationality.  Unfortunately we don’t always live in an ideal world and even the best codebases have some dust in the corners.  In our projects we have used a technique borrowed from the Norwegian dugnad to stop the rot before it becomes an issue.

What is a dugnad?

Road Cleaning

School children cleaning the roadside

From wikipediaNoun Singular: dugnad Plural: dugnads

dugnad (plural dugnads)

  1. Unpaid voluntary, orchestrated community work.

A dugnad is a norwegian tradition of working together to clean something up, usually a communal area. The idea is to get everyone together with a common goal for the common good.

How to run a code dugnad

It’s not hard to have a code dugnad, just follow these simple steps:

  • Have everyone on the team in the same room.
  • Try to focus on one area to cleanup.
  • Have a collection of small cleanup tasks prepared to get the ball rolling, preferably on a whiteboard so that the list can be updated and items ticked off.
  • Focus on communication and teamwork.
  • End with pizza. :-)

It might be useful to experiment with different durations, although from experience I’m pretty sure the optimum time is between 2 hours – 1 day.

Parting Shots

Keep in mind that a dugnad is not a license to forgo essential development practices like refactoring and it is still important to follow the boy scout rule.  The dugnad creates a forum to focus on areas of a large codebase that have been neglected or unchanged for some time, including documentation.

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Filed under quality, software, teams

C++ for Marine Streamer Positioning and Navigation

Here are the Slides from my ACCU 2011 Conference presentation.  The presentation was about how to use C++ in resource constrained devices, and building a C++ cross compile toolchain for the LM3S8962 Cortex-M3 processor.

Topics include:

  • Short introduction to the domain
  • Building a gcc cross compile toolchain
  • Programming and On-chip debugging
  • Stacks & Heaps: Linker Scripts
  • The time before “int main()”
  • C++ on a diet (living without dynamic memory allocation, the standard library, exceptions, and rtti)
  • Testable Embedded C++

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