The one UI test that matters

XCUITest: slow, brittle, but sometimes the only tool

At the very top of the pyramid sits XCUITest — Apple's UI-automation framework. It launches the actual app in a simulator, taps real elements, and asserts on what's rendered. It catches things no unit test can: did the app crash on launch, does the first screen actually appear.

It's also the slowest and most brittle layer: a simulator boot takes real seconds, and tests can break because a layout shifted, not because behavior changed. That's the pyramid lesson from Lesson 1 applied — keep very few of these.