Atomic Spin :: Elements of Software

Today I came across mention of a subversion property I was not familiar with, svn:externals. After skimming the documentation, svnbook, it seemed like something that could be useful.

What the svn:externals property allows you to do is configure a subdirectory in your project so that it is pulled from a different location in the repository, or a even different repository. Basically setting up a dependency system, albeit a simplistic one, using only subversion.

I’ve just posted a new release of Systir to Rubyforge, at the Rubyforge Systir project page. This release includes the new Mondo Pizza example web application, as seen at IQAA Quality Enrichment Conference 2005 and RubyConf 2005.

We’re working on adding significant new functionality to a legacy system. The budget doesn’t support a complete re-write. None of the legacy code has tests. The application domain is automotive testing. The particular problem at hand is controlling a throttle actuator (a simple robot that activates the throttle of a car while it’s being tested.)

The challenge

Legacy C source, 1600 lines. Many authors, 15+ years old. Complex if/else logic blocks with multiple clauses in conditionals. Several global variables. Throttle commands sent out serial port. Shared memory global variables via CPP macro interface.

How to add functionality in a TDD fashion for moving the robot smoothly?