Functional UI Testing with API Calls

Published on
October 13, 2023
Tessa McDaniel
Marketing Team Lead

UI testing and API calls are both important for your website, but combining them transforms them into a power-up!

UI (user interface) testing and API (application programming interface) testing are both fundamental parts of ensuring that your website is working properly 24/7, but wouldn’t they be more powerful if they were combined? Why, yes, yes they would! We’ll discuss UI testing and API calls separately, then look at how meaningfully combining (please feel free to skip to this juicy bit) UI or functional testing and API definitions can streamline your efficiency.

UI Testing

UI testing tests the interface of the website, but it’s also a bit more complicated than that. It covers functional and visual testing, and there are two types of UIs: command-line interface (CLI) and graphic user interface (GUI). CLIs are definitely complex, as they work by the user inputting commands through a terminal like the Command Prompt app on Windows devices. GUIs are much more intuitive with text fields, buttons to click, pretty much anything you can picture on a modern website. UI testing, for the most part, focuses on GUI testing. It tests how a website can handle actions from the mouse and keyboard, whether or not different elements like buttons and navigation bars work, usability, and so much more. 

API Calls

API is what connects the UI to the backend data part of the website using business logic. That means it determines how data is created, stored, and changed and who can access it. So API testing works on the business logic, data responses, security, and bottlenecks. With API testing, the testing phase can start before the UI is even put together to interact with. It tests how the system responds to requests from the software, not the UI. There are a lot of advantages to API testing. Generally, it is much faster than UI testing, so bugs can be found and fixed quicker. 

Putting Them Together

By combining UI tests and API calls, you move towards end-to-end testing. We want test automation that mimics (as near as possible) a real user’s journey through the app. This is why we create functional tests of the UI. But often, API calls are done in isolation, which is a good thing. There is absolutely a place for stand-alone API calls; it would be madness to argue anything else for the reasons outlined above. That said, if we want to mimic real user journeys through our application, then combining functional UI tests and API definitions gives us an approach that is greater than the sum of its parts. You can automate end-to-end journeys from a user perspective, encompassing the API layer to give a true reflection of the user experience. The advantages are multiple:

  • Cross-check front-end UI logic with API calls
  • Optimize permutations and combinations with a UI setup and API execution 
  • Enhanced defect triggering 

Now, we mentioned earlier that UI testing involves both functional and visual testing. So it would be remiss of us not to talk about combining visual regression as well (particularly when you consider that Virtuoso does that as well). Visual regression, or visual testing, validates the look and feel of the user interface against the requirements/specifications. This type of testing tends to be very manually driven, labor-intensive, and not scalable. But imagine a world where you could take your functional tests and have a snapshot of the application taken. You can then use these snapshots as a baseline and be alerted to any visual regressions. And isn’t that convenient, we’ve written a blog on just this subject!

By combining UI testing and API calls, you know everything looks on point, is functioning flawlessly, and integrates with the back end. Now that’s some serious test coverage! In lieu of having any doubts about your tests, you have the certainty of quality end-to-end testing delivers. The UI and API levels can act perfectly when separate but act up once put together. Plus, you’ll have less test maintenance by running both kinds of tests together. And wouldn’t you know it, but with Virtuoso, you can indeed run functional and visual UI tests that contain API definitions! So, why wait? Book a demo to see the cross-testing in action!


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