Test-Assisted Design

I'm re-thinking my opinions about unit tests and test-driven design. On the one hand, part of me immediately liked the idea of TDD as soon as I heard it: by writing out your tests first, you have a clear, unambiguous spec for what you're supposed to build. It's clear, because it has to be a test that the machine can run, and it's unambiguous because it's a test. It either passes or it doesn't.

On the other hand, I've been having second thoughts about unit tests ever since I saw Rich Hickey's talk on Simple Made Easy, the Magna Carta of functional programmers. Tests are good, but-- Tests are necessary, but--

The thing is, unit tests could be thought of as a kind of code smell, or a kind of technical debt. You're writing tests because you don't know what your code is going to do. And maybe that's unavoidable. Maybe programming is just too complicated for us to write code that always does exactly what we expect it to do. But still, a code smell, a sign of an undesirable circumstance that we should be trying to avoid or reduce.

Nil is not enough

Here's the context: I'm separating out all my data-store-related functions into their own namespace. Specifically, I'm working on my User model. I want to write a function that creates a new user in my data store, but only if there's not already a user with the same username. No problem, right? If the user already exists, I just return nil, the same as for any other error.

Now I'm using the create-user function I wrote above, and I pass in a user name, and I get back nil. Does that mean there was a database error (not enough space left on drive) or does that mean there was already a user with the same name? I want to get additional information out of nil, but nil doesn't contain any information. It's nil!

Setting up Friend: a few preliminaries

[Revised: found out my first diagnosis and fix were incorrect, but eventually I tracked down the real answers.]

For my summer project, I'm developing a web site that local food banks can use to let people know what items they currently need. Long term, I want this to be accessible via smart phones, but for now I'm just getting started with the basics. I'm using the Luminus framework to kick things off since it's so convenient and well-documented.

I initially set up my site with support for DailyCred, which I only heard about because it was one of the template options for creating a new Luminus project. It seemed pretty easy to set up, and I got as far as redirecting users to DC and getting back the token, but at that point DC would complain that I was using an unknown client ID (even though it was a valid ID that worked correctly in their sandbox), and I'd be dead in the water. Finally I decided to fall back to a more conventional approach: today's project is to rip out all the DC stuff and replace it with Friend. Partly this was frustration with DC, and partly it was because I just got done watching this video, and wanted to take Friend for a spin.