Adopting Test-Driven Development in Embedded Systems

Embedded software development has long been characterized by unique constraints such as limited resources, strict real-time requirements, and complex interactions with hardware. As a result, traditional software development methodologies often fail to translate smoothly into the embedded space. However, modern embedded development is evolving, and techniques like Test-Driven Development (TDD) are no longer just for web and enterprise applications: they're essential for building reliable and maintainable embedded systems.

- By Jacob Beningo

In my previous article, I introduced a modern CMake build system [1] designed to support flexible embedded development, including DevOps, simulation, and automated testing. Now, it's time to focus on one of the most powerful software engineering practices that this system enables: Test-Driven Development.

WHAT IS TEST-DRIVEN DEVELOPMENT (TDD)?

A big problem with software development is that developers write a lot of code quickly and then wait until the end to test it. Humans aren't perfect, and the chances are high that they won't catch every edge case and boundary condition. Making things worse is the fact that the testing is often done manually, so as the project grows in size, the time required to run those manual tests grows until there isn't enough time to test everything. The result is a system with bugs hiding and waiting to rear their ugly heads to users.

TDD is a development methodology that emphasizes writing tests before writing the actual implementation. Instead of blindly coding and hoping everything works at runtime, developers don't write a single line of production code unless a test is written to prove it does what it's supposed to do. There are many advantages to this approach. No code is written unless it's actually needed. All code has a test to prove that it works. Tests can be automated, which removes manual testing time

TDD enforces a disciplined approach to writing software. Developers use a simple process, which Kent Beck developed in his book Test-Driven Development. For embedded developers, though, the best interpretation of this list is the one that James Grenning put together in his book Test-Driven Development for Embedded C, called the TDD microcycle, which includes the following steps:

1) Add a small test

2) Run all the tests and see the new one fail, maybe not even compile

3) Make the small changes needed to pass the test