One question I keep being asked is, “Can we use BDD with our legacy systems?”
To help answer this, let me give my simplest definition of BDD:
BDD is the art of using examples in conversation to illustrate behaviour.
So, if you want to talk through the behaviour of your system, and use examples to illustrate that behaviour, yes, you can do this.
There are a couple of benefits of this which might be harder to achieve. The biggest is that using examples in conversation helps you explore behaviour, rather than just specifying it. Examples are easy to discuss, but it’s also easy to decide that they don’t matter, or that you can worry about that scenario later, or that you want different behaviour. It’s harder to do that when you’re talking about tests or specifications, and it’s harder still when the behaviour you’re discussing already exists. If you do find yourself talking through the different examples, you’re probably clarifying behaviour. That’s OK; just recognize that you’re doing it, so some of the usual advice we all give around BDD, and particularly around scope management with BDD, won’t apply. Asking questions, though, is still a great idea. You might find all those places where the behaviour is wrong, or annoying, or isn’t needed at all. Using examples is a great way to illustrate bugs, and helps testers out a lot.
The second aspect is the automation. (If you do this, please consider the other post I wrote about things I like to see in place first; these still apply.) Automation is usually harder with legacy systems, because often they weren’t designed with automation in mind. Websites have elements with no identifiers or meaningful classes, windows applications have complicated pieces with no automation peers, some Adobe widgets assume that if you’re using automation it must be because of reading disabilities so it will helpfully pop up boxes on your screen to ‘help’ you (thank you for that, Adobe).
But the real reason why BDD becomes hard with legacy systems is because often, the system was designed without talking through the behaviour, and the behaviour itself makes no sense.
I recently tried to retrofit SpecFlow around my little toy pet shop. The pet shop itself was designed just as a way of showcasing different automation elements, so it wasn’t particularly realistic. Because of that, I find it impossible now to have conversations about its behaviour, because its behaviour simply isn’t useful. It isn’t how I would design it if I were actually designing a UI for pet shop software. I can’t even talk to my rubber duck about it. I won’t be able to sensibly fit SpecFlow to this until I can actually change the behaviour to something sensible.
If you’re in one of those unfortunate environments with a bit of a blame culture, BDD will help introduce transparency into the quality of your process – or lack of it. Just so you’re warned. (In my instance it was a sensible trade-off at the time, since I originally wanted automation software, not a pet shop, and it’s my software so it’s my problem. You may not be so lucky.)
Automation on legacy systems can give you a nice safety net for any other changes, so it might be worth trying this for a few key scenarios. Teams and particularly testers I’ve worked with have been saved a lot of time in the past by just having one scenario that makes sure the app can start - automation is particularly useful if your build system is closer to your production system than your development one; frequently the case for legacy systems.
If you do happen to find an aspect of behaviour that you like and want to capture, then by all means, do BDD. Talk through the examples, stick them in a wiki, automate them if you can, remembering that having conversations is more important than capturing conversations is more important than automating conversations. You might even find out why things behave a certain way, and come to like the existing behaviour better.
Otherwise, you might want to wait until you’re changing the behaviour to something you like.