When I first started programming micro-processors in C, I felt like I had stepped into a time machine that took me back to my early teenage years where I spent long nights learning how to write simple programs on the C64.  But alas, after a few nostalgic programming sessions I found myself falling out of love with of procedures, modules and global variables all over again and started looking for ways to apply some of the things I have learned about software development over the last 30 years or so.

Figuring out how to use basic C++ for embedded development helped me leap about ten years ahead in time to my early twenties, where I started learning about object oriented programming in Java. But I still found micro-controller development to be slow, messy and error prone and I missed the rigour and predictability I have achieved in my programming in recent years by applying TDD.

So I started looking for information on how to write unit tests for micro-controller code and quickly came across James W. Greenings book “Test-Driven Development for Embedded C”, which convinced me I was on to something.

Although the book is choke full of good information, it is pretty sketchy on how to set up a development environment for embedded TDD, as is the documentation for CppUTest — the authors C/C++ unit testing framework of choice. And since I have never done much C/C++ development and have no prior experience with GCC, it took me a while to figure out how to set up a decent development environment on my Windows 7 PC.

I set up the environment for the Arduino because I am working on an project for this board at the moment. However, the unit testing tool chain is completely independent from the Arduino tool chain, so it should be a simple matter to adapt this setup to other boards and micro-controllers.

Step 1: Install Sublime Text with Stino

If you already have a good text editor for Arduino development, you can skip this step. However, if you are still using the standard Arduino editor, I strongly recommend that you give Sublime Text a try.

1. Download Sublime Text 2 and install
2. If you have not already done so, grab the Arudino software and install that as well
3. Open Sublime Text
4. Click the Preferences > Browse Packages… menu to open an explorer window
5. Browse up one level and then open the Installed Packages folder
6. Download Package Control.sublime-package and copy it into the Installed Packages folder
7. Restart Sublime Text
8. Click the menu Preferences->Package Control
9. Type package control install and select Package Control: Install Package
10. Type arduino and select Arduino-like IDE

You should now see an Arduino menu in Sublime Text.

Step 2: Set up the Example Project

Time to get hold of the arduino-tdd-example project and take your new development environment for a spin:

1. Open the arduino-tdd-example repository on GitHub and download the zip file
2. Unzip the project under your  Cygwin home folder (mine is c:\cygwin\home\Rasmus in the windows file system)
3. Open the helloword.ino file in Sublime Text
4. Click the menu Arduino > Preferences > Select Arduino Application Folder and select the Arduino folder on your system (e.g. c:\program files\arduino)
5. Click Arduino > Arduino AVR Boards and select the board you are using
6. Press Ctrl+Alt+V to compile the sketch

Next, try to upload the sketch to your Arduino:

1. Connect your Arduino board to your PC
2. Click the menu Arduino > Serial Port and select the Arduino COM port
3. Click the menu Arduino > Serial Monitor > Baudrate and select 9600 (this is what the example project uses)
4. Press Ctrl+Alt+M to start the serial monitor
5. Press Ctrl+Alt+U to upload the sketch to you Arduino

When the sketch has finished uploading, you should see a Hello world! message in the serial monitor.

Step 3: Install Cygwin and CppUTest

It is possible to use CppUTest with a number of tool chains but the simplest solution is probably to use Cygwin.

1. Start the latest installer from the Cygwin website
2. On the packages screen, choose to install all devel packages (they are around 500 MB, so the installation might take a while… some mirrors are faster that others though!)
3. Once the installation is complete, locate and open your Cygwin home directory in Windows Explorer (e.g c:\cygwin\home\Rasmus)
4. Download the latest release of CppUTest from the GitHub repository (I used version 3.6)
5. Unpack the CppUTest folder cpputest-x.y to your Cygwin home directory (the x.y suffix is the version number you are using)
6. Open the Cygwin terminal
7. Type cd cpputest-x.y to open the CppUtest folder
8. Type mkdir build_dir; cd build_dir
9. Type cmake ..
10. Type make
11. Finally, type make check to run the CppUTest tests

All tests should pass.

Step 4: Run the Example Unit Tests

1. In the cygwin prompt, navigate top the arduino-tdd-example project folder (use /cygdrive/c to access the c: drive in the windows file system)
2. Type make to run build and run CppUTest

And that all there is to it. Now go write some tests for your Arduino projects!