Testing Practices Interview 6: Chad Fowler
I’m very excited to have Chad Fowler as the latest participant in the Testing Practice interview series.
Chad Fowler is an internationally known software developer, trainer, manager, speaker, and musician. Over the past decade he has worked with some of the world’s largest companies and most admired software developers. He loves to program computers and, as part of his role as CTO of InfoEther, Inc., spends much of his time solving hard problems for customers in the Ruby language. He is co-organizer of RubyConf, and RailsConf and author or co-author of a number of popular software books.
And so, let’s hear from Chad…
How did you get into writing tests regularly? Did you have a specific moment when you realized automated testing was valuable?
For me it was when I was exposed to TDD for the first time. I had been practicing the typical “guru reads the output” style of testing, primarily in Java at the time. That means every class typically had a main() method at the bottom which would exercise my code and print a bunch of hardly decipherable junk to the screen. As I was developing, I knew what that junk meant. Nobody else ever did. Two days later, neither did I. But the main() methods remained. Because, hey, those were the tests.
I think the way most people worked in an environment like that is that if they needed to change anything in the production code, they would hack the existing “tests” in the main() method such that they could understand what they meant (since this stuff was embedded in production code, you didn’t typically venture out of main() for fear of polluting the namespace). So it was more of a scratchpad than a test.
At the same time, I was doing a lot of mentoring of junior developers on how to do object oriented programming. Specifically, I was trying to help a large group of developers stop generating unmaintainable spaghetti Java. I started using a technique that I call Error Driven Development. It was very much like TDD, which I had not yet heard of. You start in the area of the application you’re trying to implement. Maybe it’s a controller in an MVC setup, for example. And you type in the code you wish already existed as an API. You express your intent as clearly and succinctly as possible within the scope of what would be technically possible in this magical but not yet existing API (paying attention to which data needs to be passed around as parameters, which imaginary objects would best play the role of owning which function, etc.). Then you try to compile and/or run your code and follow the error stream until everything works.
With this kind of development, you get to always work at the level of abstraction you’re interested in while you’re developing. When I’m in a controller, I don’t care about SQL. When I’m in a view, I don’t care how business logic is implemented. To make everything run, of course, I have to walk down through the layers of abstraction and repeat this process—-imagining the perfect API and just using it. Eventually I’m done. It’s motivating and makes better code.
So, the question was about testing. This Error Driven Development technique was just a lame version of how good TDD works. TDD gives you the extra advantage of a nice framework with assertions and reports. So the first time I saw TDD, I was hooked. It was a better version of what I’d been working toward in my quest to write and help others write better code. It just happened to also create tests as a side effect.
What is your Rails testing process? What kinds of tests do you write, and what tools do you use to write them?
I use whatever testing framework and tools the team I’m working with uses. I’ve done everything from out-of-the-box test/unit to RSpec. Given a choice these days, I’d probably depend on Shoulda and Mocha. RR is really interesting as well but I haven’t fully switched to it. I suspect I might replace Mocha with it at some point in the near future.
I typically start by writing model tests. They’re called unit tests in Rails, but they’re rarely isolated unit tests. Ideally, as much logic as possible lives in the models, so I spend a lot of time here. By far more than anywhere else. I do everything test-driven unless I’m hacking something together quickly. Even then, I usually reach a point where I wish I was doing things test-driven and switch.
Ideally, your controllers are going to be tiny. They’re also likely to be composed of calls to objects and methods from your model layer. So, though I do functional (controller) tests, I try to minimize the need for them. If you’re already testing a method in a model, you don’t need to duplicate that test in a controller if the controller is simply calling the model. You do need to make sure the controller is doing its job well. That’s where things like mocks come in. I use mocks not so much to avoid calling code in the dependencies an object has (such as the classic credit card processor example) but more to allow me to specify a process in terms of what the code I’m testing is supposed to do vs. how it does it.
Ultimately, it’s a good idea for someone to actually write real automated tests. These aren’t the ones I do unless I’m playing the role of tester. For example, Selenium is an excellent tool for really testing a Rails app. It’s great to have automated tests at that level that run with a continuous build and so on. I don’t usually actually do that so it’s not part of my process per se, but I’d always advocate that it be part of a team’s process. I don’t get much value out of trying to do selenium-first development, though, for example.
What’s the most interesting thing you’ve discovered about testing recently?
I wouldn’t call it a discovery, but I’m starting to change a long held opinion about the value of tests. I used to think of them as executable requirements specifications. I know a lot of people do. I’m from the school of TDD that blossomed into what’s now called BDD. BDD people even tend to use the word “specify” when they talk about tests they write up front.
That always sounded like a great idea. Requirements docs you can execute for validity. In my experience it rarely works out that way, though. Tests don’t end up being readable like english. RSpec and especially Cucumber are a step in that direction, but I’m starting to believe that ultimately developer tests should read like good code. Maybe a little different from normal good code, but they are code after all. And they’re not for validating the production code you write. They’re for motivating the production code you write.
So maybe the goals of executable requirements documentation and motivational specs are at odds with each other. And if the tests do the job of driving you to make well designed code but don’t really read like requirements documentation afterward, that’s nothing to feel bad about.
Maybe it’s even OK to throw away the tests eventually in the same way we used to throw away the code in our main()-method scratch pads.
I’m pretty sure I’m exaggerating, but that’s the general idea.
Is there a tool you wish you had for testing, but which you don’t think currently exists?
Not really. Marcel Molina and I used to talk about how we longed for something that would sit in the middle of our objects and their method invocations, such that you could set up how you expect an object to behave and then verify, without overriding the method’s behaviors, that the object did the things you asked. Like a partial mock which doesn’t change the method implementations it’s setting expectations for.
RR now does this with its proxy implementation. Now that it exists, though I like the feature, it doesn’t feel like it filled a big hole. Go figure.
What advice would you give somebody looking to write more effective tests?
Assume that writing more effective tests means writing better code. Developer testing (which is what I do) isn’t primarily about verifying code. It’s about making great code. If you can’t test something, it might be your testing skills failing you but it’s probably your code code’s design. Testable code is almost always better code. Code written as a result of a series of failing tests is very likely (by definition) testable. (An example of a design choice in Ruby that might result from this sort of approach is to use more mixins and less inheritance.)
That being said, it’s easy to fall into a trap when you start coding this way. I often come across heavily TDD’d code with a huge focus on some trivial but easily tested feature. For example, you might start writing tests for the Ruby comparison method (<=>) or to_s on an object, simply because you know how to write tests for it. I’ve seen programmers spend a disproportionate amount of time testing and implementing ancillary features because they get the TDD (or BDD) bug and find a comfort zone to hang out in.
Instead, always focus on testing the core of your domain. Other tests are nice to have, but when you focus on the core of your domain (the features that define the product you’re implementing), you drive that domain model forward and avoid spinning your wheels on testing for the sake of testing. Kent Beck used to say “test everything that could possibly break”. That’s good advice, but I’d add “and actually matters”.
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