dtsong/regression-test-generator

Regression Test Generator

Generate a targeted regression test for a verified fix — auto-detect conventions, route to the correct test framework, annotate coverage boundaries.

Scope Constraints

• Read access to source files, test files, and package configuration
• Write access limited to test file locations (colocated __tests__/ or root tests/ directory)
• Executes test runner commands (vitest, jest, playwright) — no other shell commands
• Does not modify source code or production files
• Creates one test file per invocation — never modifies existing test files

Inputs

• FixResult (required): Path to FixResult artifact with affectedFiles, diff, diagnosis_ref, notAddressed
• DiagnosisReport (required): Path to DiagnosisReport artifact with rootCause and issueClassification
• ComponentMap (required): Path to ComponentMap artifact with component boundaries and metadata

Input Sanitization

• Test file paths are constructed from detected conventions (Step 3) and the affected component's file path. Validate that the target directory exists and is within the project. Reject paths containing .. or shell metacharacters.
• Test runner commands are constructed from detected framework names (vitest, jest, playwright) with the generated test file path. No user-provided strings are interpolated into commands.

Procedure

Copy this checklist and update as you complete each step:

Progress:
- [ ] Step 1: Read the FixResult
- [ ] Step 2: Classify Component Type
- [ ] Step 3: Detect Project Conventions
- [ ] Step 4: Generate the Test
- [ ] Step 5: Place the Test File
- [ ] Step 6: Validate the Test

Note: If you've lost context of previous steps (e.g., after context compaction), check the progress checklist above. Resume from the last unchecked item. Re-read relevant reference files if needed.

Step 1: Read the FixResult

Extract from the upstream FixResult:

• affectedFiles — the files that were changed
• diff — what changed (the fix)
• diagnosis_ref — the original bug description
• notAddressed — related issues not covered by the fix

Step 2: Classify Component Type

Determine the routing target. This is a hard rule:

| Component type | Detected by | Route to | |---|---|---| | Sync client component | "use client" directive, uses hooks, event handlers | Vitest + RTL | | Sync server component | No "use client", no hooks, no async | Vitest + RTL | | Async server component | async function Component(), await in body, fetch() / cookies() / headers() | Playwright E2E | | Mixed (client wrapper around async server) | Both patterns present | Playwright E2E for the page, Vitest+RTL for the client wrapper |

If async server component → read references/playwright-patterns.md. Otherwise → read references/vitest-rtl-patterns.md.

Step 3: Detect Project Conventions

Scan for existing test files near the affected component:

1. Glob: **/*.test.{ts,tsx}, **/*.spec.{ts,tsx}, **/__tests__/** in the same package
2. Pick the nearest test file to the affected component (same directory > parent > sibling)
3. Extract from that file:
   • Import style: @testing-library/react vs custom test-utils wrapper
   • Render pattern: bare render() vs custom render with providers
   • Query preference: getByRole vs getByTestId vs getByText
   • File location: colocated (__tests__/ or .test.tsx next to component) vs root tests/ dir
   • File naming: ComponentName.test.tsx vs component-name.spec.tsx
4. If no existing test files found, note: "No existing test conventions detected. Using @testing-library/react defaults." Use colocated .test.tsx naming.

Step 4: Generate the Test

Write the test file following detected conventions. Every generated test must include:

Header annotations (mandatory):

/**
 * Regression test for: [bug title from DiagnosisReport]
 * Bug: [1-sentence defect description]
 * Fix: [1-sentence fix description]
 *
 * GUARDS AGAINST: [specific scenario this test catches]
 * DOES NOT GUARD AGAINST: [related untested scenarios from notAddressed]
 */

Test structure:

describe('[ComponentName] - regression: [bug-slug]', () => {
  it('should [expected behavior that was broken]', () => {
    // Arrange: conditions that triggered the bug
    // Act: user action that exposed the bug
    // Assert: correct behavior
  });
});

Anti-brittleness rules (hard constraints):

• No snapshot tests — use explicit behavioral assertions
• Prefer getByRole with accessible name: getByRole('button', { name: /submit/i })
• Use screen object, not destructured render returns
• Mock at system boundaries (API, external services), not internal functions
• Assert user-visible outcomes ("error message appears"), not internal state
• No DOM structure assertions (querySelector('.a > .b'))
• No class name or CSS property assertions

Step 5: Place the Test File

Follow the convention detected in Step 3:

• If colocated pattern: place next to the component file
• If root tests/ pattern: mirror the source directory structure
• Use the detected naming convention (.test.tsx vs .spec.tsx)

Show the full file path and contents. Pause: "Write this test file?"

Step 6: Validate the Test

After writing the test file, run it once:

# Vitest
npx vitest --run --reporter=verbose <test-file>

# Jest
npx jest <test-file> --verbose

# Playwright
npx playwright test <test-file> --reporter=list

Report result:

• Test passes: "Regression test passes. It verifies [behavior]. Run it before future changes to [component] to catch regressions."
• Test fails: "Test failed — this may indicate the test needs adjustment. Error: [message]." Do not auto-fix. Show the error and let the user decide.

Output Format

RegressionTest:
  version: "1.0"
  fix_ref: "[FixResult ID]"
  testFile: "path/to/ComponentName.test.tsx"
  framework: "vitest-rtl | jest-rtl | playwright"
  guardsAgainst: "specific regression scenario"
  doesNotGuardAgainst: ["untested scenario 1", "untested scenario 2"]
  conventions:
    source: "detected | defaults"
    nearestTestFile: "path or null"
  result: { status: "pass | fail", error: "message or null" }

Handoff

Pass the RegressionTest artifact path to qa-coordinator. The result contains testFile, framework, guardsAgainst, and doesNotGuardAgainst fields. This is the final phase of the QA pipeline.

References

| Path | Load Condition | Content Summary | |------|---------------|-----------------| | references/vitest-rtl-patterns.md | Step 2, sync client or server component | Query priority, rendering patterns, assertion patterns, anti-patterns | | references/playwright-patterns.md | Step 2, async server component or mixed | Test structure, locator priority, common regression patterns, API mocking |