React and Next.js Regression Test Coverage
Generate React and Next.js tests with Jest, Testing Library, MSW, and Playwright, prioritized by regression risk.
Before & after
Same prompt, same agent — the only difference is the skill.
I can help you write tests for your React checkout component. A good test suite would cover: - Rendering with different props - User interactions like clicking and typing - Form validation - Success and error states - Edge cases like empty cart You'd typically use Jest with React Testing Library for component tests. For end-to-end flows, Playwright or Cypress works well. Mocking the API calls is important so tests are reliable. Share the component and I can suggest specific test cases.
TEST SUITE — React checkout. Generated by scanning the component, not guessing at it. Three layers, because checkout needs all three. UNIT (Jest + React Testing Library) — from the component's actual props ✓ renders line items from cart prop ✓ disables "Pay" when cart is empty ✓ shows validation error on invalid card, no submit ✓ calls onSubmit with the right payload on valid input API calls mocked with MSW — so tests don't hit a real endpoint and aren't flaky. E2E (Playwright) — scaffolded from your Next.js routes ✓ /cart → /checkout → /confirmation happy path ✓ declined-card path shows the error state, stays on /checkout These are the ones that catch the real checkout bugs — the button that works in a unit test but is off-screen in a real browser. COVERAGE-DRIVEN GAP FILL Reads your Istanbul/LCOV report and surfaces what's UNtested — so you're not writing your 40th happy-path test while the error branch has zero coverage. The gaps are where the bugs live. FIXTURES A cart fixture (empty, one item, many items) reused across all tests, so a data-shape change is one edit, not forty. THE ORDER THAT MATTERS Unit for logic, E2E for the money path, coverage report to find the holes. On checkout, the declined-card E2E is the test I'd write first — it's the one that costs revenue when it breaks. Point me at the component and your route folder and I'll generate the stubs.
About this skill
Your coverage percentage goes up, but checkout still breaks. This skill reads the actual React or Next.js behavior, identifies the failures worth catching, and writes tests at the layer that can expose them.
What it does
- Writes Jest and React Testing Library tests for validation, loading, errors, successful submissions, and prop-dependent behavior.
- Uses MSW to exercise real request construction and response handling, with isolated handlers and fixtures.
- Reads Istanbul and LCOV reports to distinguish uncovered lines, branches, and functions, then prioritizes gaps by regression risk.
- Builds Playwright tests from actual Next.js routes, including concrete dynamic parameters, authentication setup, and observable outcomes.
- Detects testing boundaries around async Server Components, server-side requests, hydration, and browser-only behavior.
- Fits test configuration into the existing project and diagnoses flaky assertions without hiding failures behind retries.
What you get
Tests or focused patches, any necessary setup changes, and a short explanation of which failures each test catches. Validation is reported as executed, failed, or proposed, with remaining coverage limits stated explicitly.
Best for
Teams maintaining React and Next.js applications that need meaningful coverage for existing features, API-driven components, critical routes, or a suite that passes while real regressions escape.
SKILL.md preview
---
name: react-and-nextjs-regression-test-coverage
description: Generates React and Next.js regression tests with Jest, React Testing Library, MSW, and Playwright by mapping observable behavior and coverage gaps to the cheapest reliable test layer. Use when the user says "generate tests for this component", "our coverage is high but bugs keep escaping", "analyze this LCOV report", "mock these API calls", "set up Jest for Next.js", "scaffold Playwright tests for these routes", or "my form tests keep passing when submission is broken".
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# React and Next.js Regression Test Coverage
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