Motivation
The Page Object Model (POM) has been the de facto standard in UI automation using Selenium for years now. Here* is a typical primer on the subject. This primer does a perfectly reasonable job of showing how people normally use POM, and it also clearly shows the reason that using POM the way I've seen a lot of people use it is insufficient for writing maintainable tests.The problem is illuminated in the author's 5th reason for using POM: "Any change in UI can easily be implemented, updated and maintained into the Page Objects and Classes." If you've done this for a while, you'll notice what is not said here - that a change in business process or higher-level user interaction with the site cannot be easily implemented in our automation. For that type of change, if we were to only use POM, we'd have to update all of the related tests. That is to say, this style of POM is sufficient for encapsulation and maintainability of UI elements and structure, but we need something higher-level to encapsulate and maintain business processes.
Typical POM
As a trivial example, let's say you have this PO class and test:You're going to have hundreds of other tests that contain this same login code of course. What happens when the id of the username field changes? With POM, you're golden. You just update the username element on your LoginPage class. But what happens when there's a new step in logging in? Now all of your tests have to change to look like:
As an automation developer, you can be certain that your site will change - and not just in rearrangement or renaming elements on a page. Some people will say "Hey, I've got a method called login() in my LoginPage class, so that's all I'll have to update." Well kudos, you're a big step closer, let's check it out. We have the login() method to our LoginPage class, so all we do is add the element and the line in the login() method. While we're at it, we'll put the goto() in there. That way our test will be super clean and maintainable:
You will be good to go for this trivial example. But what about when your company decides to change a business process in your app? Let's say you want to add a step in a checkout process such as buying a couch. In the past, you had the code below... you were smart so you even wrapped clicking submitButton with a method, not wanting to mix the use of PO methods like loginPage.login() and use of the PO elements themselves like loginPage.submitButton.click():
The Issue...
The problem is that we're still modeling the interaction with the UI - we're focused on the website. What we should be modeling is what the user wants to do. The user doesn't want to select from a dropdown on pageA and click some buttons on pageB, they're trying to buy a couch, and we're not encapsulating that anywhere, except arguably in the test. That's too late, because we're going to have dozens of really similar tests where the user just wants to do a tiny thing different, such as choosing express shipping vs. regular shipping, so all that test code is going to be duplicated, and we're not going to be DRY at all.In this example our app changed, and now we have an "assembly and delivery" step. All our tests have to change again:
Flow classes
The Flow class is intended to do this encapsulation and abstraction for us. It models what the user is trying to accomplish (user stories?) when they're using your application. Let's check it out:And now your tests can model the use cases, and they simply looks like:
So maybe the title of this post shouldn't be Flow vs Page Objects, because both layers are useful and work together. The POs encapsulate the UI, and the Flow encapsulates the business rules. Then the tests simply encapsulate the use cases. Honestly, if your app is small enough, like a mobile app, you can do both in the Flow class. I've done this successfully, but a UI refactor probably would have cost me more than if I'd done a proper PO layer.
Looking at the test case, you probably see the potential problems:
- The more work we make our methods do, the more data we have to pass in to let them know how to do it. For this, we'll have to start consolidating data elements into their logical groups. I'll talk about that in the next post here.
- Using flows works great for positive tests, but what about negative tests? I'll talk about that in this post.
