#ifdef

There’s been a long running conversation about the relationship between static typing and unit testing. As early as 2003, Bob Martin found that unit tests reduce dependence on type safety. Around the same time Bruce Eckel argued that compilation is simply one test for correctness; and that code needs to pass all the tests that define correctness of your program. More recently, Stuart Halloway claims ‘In 5 years, we’ll view compilation as the weakest form of unit testing‘. Are you spotting a trend here?

This all bubbled up again for me recently on an embedded project I’m working on to optimize security policy lookups on a multicore security platform. The task was to optimize performance of the vendor’s C reference implementation. Policy insertion used a simple, but unscalable single linked list having O(n) performance. Of course, the code comes without tests of any kind, so how does one know that the optimization changes don’t break basic functionality?

Obviously, the best thing to do in this situation is to write tests for existing behavior so that as the API is refactored and reimplemented, the tests find any new logic errors. I got payback even before the optimization work got started. The linked list insert (implemented thousands of times by thousands of developers) had a bug in it. Policies that were supposed to be stored in priority order after insert were off by one.

Definition: Reference System n. A software implementation provided by hardware vendors to demonstrate programming of a target device; not intended for deployment in end user products. (2) A software implementation provided by hardware vendors that is for the most part, directly inserted into the systems of end users.

This really isn’t a rant about reference code, it’s about defensive testing and the fact that writing tests are not just for dynamic languages. The Java community is mostly on board with this, but it seems to have gotten slower adoption by the C variant world. So c’mon embedded developers. Let’s stop pretending that the type safety testing by our compilers is good enough.

Here’s one option. I really like check as a unit test tool for C. It has a niced xUnit flavor and ought to be in everyone’s toolbox.

START_TEST(it_should_insert_in priority_order)
{
    Policy* policy5 = alloc_policy_with_priority(5);
    Policy* policy6 = alloc_policy_with_priority(6);
    insert_policy(policy5);
    insert_policy(policy6);
    fail_if(policy_find(policy5) == NULL);
    fail_if(policy_find(policy6) == NULL);
    fail_unless(policy_first() == policy5);
}
END_TEST

And if you happen to be implementing reference code, a set of tests for your API would be a welcome addition to your product; not a program to exercise the hardware, but tests that verify and document the behavior of your APIs. It will reduce the bulk of documentation that needs to be provided to end users and may allow you to remove those weasel words, “not intended for deployment”.

Exactly who hired the B players then?

“A players hire A players,” he said. “B players hire C players. Do you get it?”

[From Folklore.org: Macintosh Stories: How to Hire Insanely Great Employees]

It turns out that some changes to the Linux kernel — Ubuntu 8.04 uses Linux 2.6.24 — have introduced some issues that make running Ubuntu in a VMWare virtual machine difficult. Ubuntu will install just fine, but you won’t have access to VMWare Tools, which provides some nice features like shared folders and clipboard syncing.

[From Ubuntu 8.04 Causes Problems With VMWare Tools, Open Source to the Rescue | Compiler from Wired.com]

It isn’t just VMWare. Mac Parallels has likewise bitten me and many others judging by the considerable forum angst. My peeps have been telling me to cutover to Fusion. I’d say if VMWare fixes their tools issues before Parallels, I’ll consider it.

I’m intrigued by the number of casual conversations lately that have touched on the theme of embracing constraints as a gateway to creative solutions. Are artists as constraint infected as their tech world brethren? There seems to be an awareness that unrestricted composition is a daunting task and that introducing constraints can get you to the downbeat.

Instead, someone says, “Write me a piece of music using only a flute, saw, and this broken toy piano. You can only use the notes D, E, and B – but never all 3 at the same time. It has to be in 3/4 time, start quiet, get loud, then get quiet by the end. Go!”

Aha! Now you’re cookin’!

[From Restrictions will set you free | Derek Sivers]

Recently, I’m hearing folks talk about their timed dashes. Duff says Nokahuna was a 48 hour burst effort and Nathaniel is crafting his weekly schedule to create artificial calendar constraints.

There, I did it. A blog post constrained to three paragraphs, a quote plus six links that associate 37signals with a broken toy piano. How’s that for a creative solution?