If you're building Umbraco backoffice extensions and need to test error states, loading spinners, or edge cases without spinning up a full backend, this is your setup guide for MSW (Mock Service Worker). It walks through the MSW v2 syntax with concrete handlers for GET/POST/PUT/DELETE, shows you how to simulate 404s, 500s, validation errors, and delayed responses, and includes the full web-test-runner configuration with import maps for Umbraco's Lit-based components. The mock database pattern is clean, and the umbracoPath helper keeps your API routes consistent. It's thorough on the mechanics but assumes you already know why you'd want API mocking in your test suite.
npx -y skills add umbraco/umbraco-cms-backoffice-skills --skill umbraco-msw-testing --agent claude-codeInstalls into .claude/skills of the current project.
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