test-snapshot_skill

Overview

This skill helps teams create snapshot and golden tests to detect unintended output changes across UI, APIs, and serialization contracts. It defines a practical checklist, change-detection strategy, and a prioritized test plan to focus effort where it prevents regressions. The goal is repeatable baselines that integrate with CI and a review workflow for intentional updates.

How this skill works

The skill guides capture of deterministic baselines: visual snapshots for component states, API response baselines, and serialized model outputs. It prescribes excluding volatile fields, setting pixel tolerances, and organizing diffs for clear failure triage. It also recommends CI gating and grouping snapshots for batch approval when schema changes are intentional.

When to use it

• When introducing UI components or updating visual states (themes, densities, interaction states)
• When stabilizing API surface contracts or adding new endpoints
• When evolving serialization formats (JSON, XML, Protobuf) that must remain compatible
• When hardening release pipelines to block regressions via CI snapshot checks
• When onboarding a review process for intentional baseline updates

Best practices

• Capture all relevant UI states and test across viewports and densities to catch platform-specific regressions
• Exclude or normalize volatile fields (timestamps, generated IDs) before comparison to avoid noise
• Set and document pixel tolerance thresholds for visual tests to allow acceptable rendering variance
• Record and version baselines per API version and include header/content-type checks
• Integrate snapshot checks into CI and require human review for baseline updates

Example use cases

• Create visual snapshots for a button component across default, hover, focus, disabled, and high-contrast modes
• Record API success and error response baselines, including pagination envelopes and headers
• Snapshot model serialization for backward compatibility when adding or deprecating fields
• Block merges in CI when snapshot diffs appear until a reviewer approves intentional changes
• Group related schema changes and update multiple golden files together with a documented approval note