Relevance Craftsman Swap Day 3

Day 3 at Relevance began, as the previous days, with the company standup. Stuart Sierra, of clojure.test and Practical Clojure fame, was my pair for the day.

Yep, there are two Stuarts at Relevance with Clojure books! If you’re interested in Clojure, and you haven’t already purchased the Apress book, electronic or print, you should do that.

We started off with some Bash scripting for a cron job. Mostly pretty straightforward stuff, though I did really like the way the structure and logging behavior in the script turned out. I won’t go so far as to say that this (or any) Bash script is a thing of beauty, but it’s very clear, concise, and is going to do the job very well.

One cool thing I hadn’t realized was possible (and Stuart mentioned that a decent amount configuration is necessary for this) is that we used sendmail to, well, send mail—but directly from the command line. So we had something along these lines:

1 message = "cat email_file_contents.txt"
2 sendmail -t $message

Our needs weren’t very complex with regard to things like email headers, so it really was dirt simple to use, which was a very pleasant surprise.

We worked in Emacs, which was a bit of a struggle for me. But it was a reminder that I ought to be able to use it better, as I’m interested in Clojure and many people in the community are gung ho about it.

One notable takeaway was org-mode—we used the tables there to structure our table-based tests, and it can do some pretty cool formatting. I’ll also say in Emacs’ favor that users and authors sure are serious about documentation, which I love to see. However, it can be a bit intimidating when you feel like you have to read a few books to get to know the editor.

At the project standup with Stuart, Alan Dipert, and Shay Frendt, the client reported a problem with a story that’s still in progress, so Stuart and I spent the remainder of the day chasing this bug.

There were several bright spots, however. We added several higher level tests around some data translation layers of the system (which includes JRuby on Rails and Clojure applications). Our tests were on the Clojure side of things, which was great to get a chance to see.

Stuart had this great idea to write table based tests a la Cucumber or FitNesse. We wrote a quick and dirty parser for a syntax similar to Cucumber’s, plumbed a few tests in, and found one of our problems after a bit of data correction.

We found the other, more mysterious problem soon afterward, and spent most of the rest of the day trying to track down the exact reason for it. It’s interesting that neither of these problems had much to do with code, as they were both problems with data. In one case, we received data in a format we didn’t expect, and in the other, a subset of data went missing.

I generally feel like good practices like TDD and pair programming can save you from many unexpected errors, but I don’t know that there’s a good solution for cases where data is mucked up, besides deploying, seeing what real data looks like, and adapting based on those results.

I would suggest something like Haskell’s QuickCheck to try out more possibilities in the tests, but even if we used something like that here, I have a feeling we would have still ended up with an incorrect constraint, so wouldn’t have caught these problems.

These problems make me wonder if, as external data drives more and more of a given application, it becomes more and more important for the data itself to be tested. That is, it would be ideal to be able to write tests that make assertions against the structure and contents of the external data.

I’m not sure whether that would have been possible in this case, due to privacy concerns, but it’s an idea that I’d love to hear feedback on anyway. And now that I imagine such a test system more carefully, maybe that’s just design by contract in a different light?

I’m Looking forward to tomorrow!

Colin Jones, Director of Software Services

Colin Jones is particularly interested in web security and functional programming, using languages like Clojure.