Previews and tests

Previews and tests

Use previews to design and to check by eye: one preview for each state, with sample data, in both color schemes and at several text sizes. Use unit tests for logic that lives outside views — models, formatting, navigation paths — which is the reason that logic should not sit inside body. Use UI tests sparingly, for a few flows you cannot afford to break, and snapshot tests if you need to catch visual regressions.

Interviewers often ask how you test SwiftUI views. A good answer: keep views thin, test the model, check rendering with previews or snapshots, and cover a few complete flows with UI tests.

For one screen, write previews for its empty, loading, loaded, and error states, and unit tests for the model that drives them.

1. What belongs in a unit test, and what belongs in a preview?
2. How would you test a SwiftUI view?
3. Why does keeping logic out of body matter for testing?

• Previewing your app’s interface in Xcode
• Swift Testing
• WWDC26: Migrate to Swift Testing