How to Speed Up SwiftUI Development and Testing Using PreviewSnapshots
Article Summary
John Flanagan from DoorDash reveals how his team eliminated duplicate code between SwiftUI previews and snapshot tests. The solution? An open-source tool that cuts testing boilerplate to a single line.
DoorDash's iOS Infrastructure team built PreviewSnapshots to solve a common pain point: developers were writing nearly identical code twice when using Xcode Previews for rapid UI iteration and SnapshotTesting for visual regression testing. The tool lets teams define view states once and reuse them across both workflows.
Key Takeaways
- Single test assertion replaces multiple individual snapshot test functions
- Complex views with multiple bindings benefit most from reduced boilerplate
- New preview configurations automatically generate corresponding snapshot tests
- Open-source library integrates with Point-Free's SnapshotTesting framework
PreviewSnapshots eliminates code duplication by letting developers write view configurations once for both Xcode Previews and snapshot testing, with automatic test generation for each preview state.
About This Article
SwiftUI developers at DoorDash were duplicating code when they tried to use Xcode Previews alongside SnapshotTesting. They had to write separate implementations for preview configurations and individual snapshot test functions for each view state.
John Flanagan's team built PreviewSnapshots, a generic tool that takes a collection of configurations and a configure closure. Developers define view states once using the NamedPreviewState protocol, and the tool generates both previews and tests from that single definition.
Complex views with multiple Bindings and arguments benefited most. Instead of writing multiple snapshot test functions, developers could call assertSnapshots() once and it would test all preview configurations against reference images on disk.
