UI testing
Functional testing asks whether a feature does the right thing, does a checkout flow correctly calculate a total. UI testing asks something narrower, does the interface itself render and behave correctly, does a button appear where it should, is it clickable, does a layout hold up at different screen sizes, does an error message actually show up where a user would see it. The two overlap heavily in practice, a single automated test often checks both at once, but the distinction matters when deciding what a specific test is actually for.
A few things get checked specifically. Visual correctness, whether an element renders where and how it's supposed to, without obvious layout breakage. Interactivity, whether a button, a dropdown, or a form field actually responds to a click, a selection, or input the way it should. State changes, whether the interface updates correctly after an action, like a cart count incrementing after adding an item. And consistency across the application, whether a component that appears in multiple places looks and behaves the same everywhere it shows up.
This is largely driven by browser automation tools like Selenium, Playwright, or Cypress for web applications, often paired with visual regression tooling that compares a screenshot against a known-good baseline to catch a layout change a purely functional assertion wouldn't notice. Because the UI is also the layer most likely to change frequently, through redesigns and iteration, UI tests also tend to be the ones that break most often for reasons that have nothing to do with a real defect.
What gets checked
- Visual correctness, whether an element renders where and how it's supposed to, without obvious layout breakage.
- Interactivity, whether a button, dropdown, or form field actually responds to a click, selection, or input.
- State changes, whether the interface updates correctly after an action, like a cart count incrementing.
- Consistency, whether a component that appears in multiple places looks and behaves the same everywhere it shows up.
Where it shows up
- Confirming a button is visible, enabled, and clickable in the state it's supposed to be in.
- Catching a layout break after a CSS change, using visual regression tooling against a known-good baseline.
- Verifying a form shows the correct validation message in the correct place after an invalid submission.
- Checking that a shared component, like a navigation bar, looks and behaves consistently across every page it appears on.
Benefits and challenges
| Benefit | Challenge |
|---|---|
| Catches a problem users would actually see and be frustrated by, a broken layout or an unresponsive button. | Tightly coupled to the interface's current structure, so UI tests tend to break the most often as the design changes. |
| Visual regression tooling catches a layout issue a purely functional assertion, checking only data or logic, would completely miss. | A visual diff can flag a harmless, intentional change as a failure, creating noise that needs a person to review and approve. |
| Can be automated across browsers and devices, giving broad, repeatable interface coverage. | Slower to run than lower-level tests, since it generally requires a real or simulated browser rendering the full page. |
Frequently asked questions
What's the difference between UI testing and functional testing?
Functional testing checks whether a feature's underlying logic produces the right result, like a checkout flow calculating the correct total. UI testing checks the interface layer specifically, whether elements render, respond to interaction, and look right. A single automated test often checks both, but they're asking different questions.
What is visual regression testing?
It's a specific technique within UI testing that compares a screenshot of the current interface against a known-good baseline image, flagging a difference for review. It catches a layout or styling break that a purely functional assertion, which only checks data or behavior, wouldn't notice at all.
Why do UI tests break so often?
Because the UI is usually the part of an application that changes most frequently, through redesigns, new components, and iteration. A UI test tied to a specific selector or layout detail breaks whenever that detail changes, even when the underlying feature it's meant to check still works correctly.
How Klarent helps
Klarent's AI agents recognize an interface element by what it does rather than a fixed selector or exact layout position, so a UI test keeps working through a redesign or a minor styling change instead of breaking on every visual tweak.