Saturday, 22 September 2012

In which the general fear of TDD is discovered

Since I last wrote about test-driven development—since we spent that time at work learning how to do it, I’ve been trying to make use of it in my off-time development. I’ve mentioned before that I’ve been writing an ORM from scratch, to satisfy an itch that I have. In its current incarnation, I haven’t really had many opportunities to write anything using it, other than an aborted attempt to create a tracker for the No-Cry Sleep Solution.

Earlier this year, the note-taking web app that I’ve been using for years made a major overhaul of their user interface…and left mobile web out in the cold. Seriously. If you aren’t accessing the site from something that can fully act like a desktopfull-scale browser, then you’d better be on either an Android or iOS device, because otherwise, you’ve been left out in the cold.

At the time, I was well and truly in the cold. My mobile phone was, and still is, a Palm Centro. My only tablet-like device was my Kobo Touch (my wife owns a Nook Color, but I wasn't about to both commandeer it during the day and install a note taking app), though we’ve since also purchased an iPad with LTE. At work, at the time, I used my Kobo to present myself with my notes during scrums. Since then, I’ve been writing to a static HTML file on those days that I don't bring the iPad to the office, but there’s still a nontrivial issue of synchronisation. While I could probably use Dropbox and a reasonably simple PHP application to read and write to a single note file, that still just doesn’t do it for me.

So, I opted to begin writing my own, using Alchemy and Zend Framework on the back end. The initial progress wasn't so bad, and it isn’t as though I didn’t have alternatives that have worked reasonably well in the meantime. I decided to basically cater to my own use cases, since I could. Mobile Web would be reasonably fully featured, if a degraded experience. My Kobo Touch would get a good interface where I could edit notes, or write new ones, easily. It would all be there.

The problem is that it hasn’t always been smooth sailing. Ignoring the fact that I don’t often have the opportunity to work on it at home, having a toddler, it seems like with every model I implement, I find another thing about Alchemy that needs to be added or fixed. I’ve been trying to adhere to test-driven development to do that, but by God, I made it difficult to do that in some places. Doing the whole “TDD as if you meant it” thing can be particularly tricky when you’re working with an existing codebase that isn't particularly (or even remotely) tested, and particularly when you're writing web application controllers. Controllers are notoriously hard to unit test, if for no other reason that because their very purpose is side effects, which runs somewhat contrary to many of the premises of test-driven development. I’m finding that it’s far more straightforward to perform acceptance testing on your controllers, and actually go through the motions of the task you’re seeking to test.

Where I’ve been running into difficulty with Project Seshat,¹ though, is in code that I not only wrote a long time ago (somewhere on the order of three years), but also works perfectly well in isolation. The Model class, and its database-driven subclass, provide a parent class to all model-like activity in my application. It acts as entity, DAO, and service layer, mainly because that’s what made the most sense to me at the time I started writing it (this was well before I started working with enterprise Java. I still disagree with the notion of the DTO, but have yet to fully articulate why, to my own satisfaction). And that’s fine; it can still work reasonably well within that context. The problem is that, at some point when working with each of the last two Models I’ve added, the logic that stores the information in the database has both succeeded and failed in that regard at the same time.


One of the core features of the ORM in Project Alchemy is that every change that’s written to the database with an expectation of long-term persistence (so, basically, everything that isn’t session data) also gets logged elsewhere in the database, so that complete change history is available. This way, if you ever need to figure out who did something stupid, it’s already there. As a developer, you don’t have to create and call that auditing layer, because it was always there, and done for you.

This audit trail, in its current form, is written to the database first—I decided to implement write-ahead logging for some reason that made perfect sense at the time. Not that it doesn’t make sense now, but there are a lot of features that still have to be implemented…like reading from this log and providing a straightforward function for reverting to any previous version. But at least the data will be there, if only, for now, for low-level analysis.

At any rate, because I can see these audits being written, I know that the ORM is at least trying to record the changes to the entities that I've specified; they’re available at the time that I call the write() method in the storage area for uncommitted data. The pain is that when it tries to create a new instance of the Model in the database, the model-specific fields aren’t being written to the entity table, only to the log. The yet-more painful part is that this doesn’t happen in testing, when I try to reproduce it in a controlled environment. This probably just means that these bug-hunting tests are insufficient; that they don’t fully reproduce the environment in which the failure is occurring.

So yeah. TDD, while it’s great for writing new code, is very difficult to integrate into existing code. I’ve had to do what felt like some strange things to shoehorn a test fixture in place around all this code I’ve already written. I recognise that the audit trail makes the testing aspect a little bit more difficult, since it's technically a side-effect. However, I don’t really want to refactor too much, of any, of the Model API, simply because my IDE isn’t nearly clever enough to be able to do it automagically, and because I still really, really want the audit trail to be something that doesn’t have to be specifically called.

I am, however, beginning to understand why so many developers who have never really tried TDD dismiss it, claiming that you end up writing your code twice. At first, you think that the test and the code are completely distinct entities, and that the structure of your tests will necessarily reflect your code. Yeah, this would mean that you’re doing everything twice. But that’s not TDD done properly. But then when you get into it, you realise that it isn’t the new code you have to write twice, but all the existing code that has to be massively refactored (and in some cases, virtually rewritten, so dissimilar is the result from the what you started with), and that’s always a daunting thought. You may even find yourself feeling compelled to throw out things you’ve spent a great deal of time and effort on, purely in order to get it testable.

I get that. That’s where I am right now. But there are two things to remember. First of all, your code is not you. If you want to work effectively in any kind of collaborative environment, whether at work or on an open-source project, you need to be able to write code and leave your ego at the door. Hell, the same thing goes for personal projects. The second is that if you refuse to make something better (whether better means more efficient, more maintainable, or whatever), simply because you invested x hours in it is foolish. You probably made something good, but you can always make it better if you’re willing to put in the effort.

And speaking of persistence issue, I’m sure I’ll fix it eventually. I already did once, though I didn’t properly record how I did it. Gee, if only I had some kind of mechanism for taking notes!

¹ Seshat was the Egyptian goddess of wisdom, knowledge, and writing. Seems appropriate to use a name that means "she who scrivens" for the tool you're going to use for your own scrivening.

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