petrkindlmann Before starting: Check for .agents/qa-project-context.md in the project root. It contains test framework conventions, naming patterns, and project-specific quality standards that calibrate review feedback.
Quick Route
Three distinct entry paths. Pick the row, then jump to the named section.
| Situation | Path | Jump to |
|---|---|---|
| PR with changed test files | Run the changed files, score them, check the diff against the PR checklist | Verification → PR Review Checklist |
| Whole suite needs a health pass | Quantify, sample, find the 3-5 systemic smells, propose lint/mutation gates | Batch Audit Process |
| Application code, "why is this hard to test?" | Flag DI / side-effect / pure-function / interface problems with before/after | Testability Analysis |
All three share the same smell vocabulary (the six buckets below) and the same Verification commands.
Discovery Questions
First, read .agents/qa-project-context.md if present and skip any question it already answers.
- Review scope: Reviewing test code for quality, application code for testability, or both? Each triggers a different Quick Route path.
- Framework conventions: What test framework (Jest, Vitest, Playwright, pytest)? Conventions differ —
describe/itnesting, fixture usage, assertion style — and the Verification commands are per-framework. - PR review or batch audit? A PR review runs and scores only the changed files. A batch audit scans the entire suite for systemic patterns.
- Existing quality standards: Does the team have documented test conventions? Check for
.eslintrctest rules,CONTRIBUTING.mdtest guidelines, or a test style guide. - Known pain points: Recurring flaky tests, slow suites, unclear failures? These prioritize which smells to focus on first.
Core Principles
Test code is production code. Apply the same quality standards: readability, maintainability, single responsibility. Test code that is hard to read is hard to trust.
Review what is asserted, not just what is executed. Coverage proves a line ran; it says nothing about whether a wrong value would be caught. A 95%-coverage suite of
toBeTruthyassertions catches almost nothing. Mutation score (see Verification) measures the thing coverage can't.Testability review prevents test debt. Reviewing application code for testability catches design problems before they force awkward test workarounds. If code is hard to test, it is usually hard to maintain.
Codify patterns, not just knowledge. Turn recurring review feedback into lint rules, custom ESLint plugins, or shared fixtures. Reviews that repeat the same feedback indicate missing automation.
Smells are symptoms, not verdicts. A test smell indicates a potential problem; context decides whether it is actually harmful. A long test for a complex workflow may be appropriate. A mock-heavy test for a boundary may be correct.
Actionable feedback only. Every review comment must include what is wrong, why it matters, and how to fix it. "This test is bad" is not actionable. "This test uses sleep-based waiting which causes flakiness — replace with an explicit wait condition" is.
Test Smell Buckets
Six dimensions. Each smell is categorized by the dimension it affects and links to a specific review action. Full SMELL/FIX code for every catalogued smell lives in references/smell-examples.md — keep the inline pointers prominent; the before/after code is the load-bearing part.
Readability Smells
Problems that make tests hard to understand at a glance.
Obscure Setup
What it looks like: 30+ lines of object construction with irrelevant fields drowning the test intent. The reader cannot tell which fields matter for the assertion.
Fix: Extract to factories. Only test-relevant data should appear in the test body: buildOrder({ items: [buildItem({ weight: 2.5, quantity: 2 })] }) instead of constructing full user/product/order objects inline.
Review action: Request factory extraction.
Mystery Guest
What it looks like: loadFixture('report.json') — the test depends on external data the reader cannot see. They must open another file to understand the assertion.
Fix: Inline the test-relevant data or use descriptively named fixtures. The reader should understand the test without opening other files.
Review action: Request inline data or descriptive fixture names.
Duplicate Assertions
What it looks like: Multiple tests assert the same behavior with varying specificity (toBe('Alice'), toHaveProperty('name'), toBeDefined()). Three tests, one behavior.
Review action: Request consolidation. Keep the most specific assertion. Redundant tests increase maintenance cost without increasing confidence.
Reliability Smells
Problems that cause tests to fail intermittently or in unexpected environments.
Sleep-Based Waiting
What it looks like: setTimeout, sleep(), waitForTimeout() used for synchronization. See references/smell-examples.md for the SMELL/FIX pair (replace waitForTimeout with an explicit toBeVisible wait).
Review action: Reject. Sleep-based waiting is never acceptable. Require explicit wait conditions.
Order Dependency
What it looks like: Tests pass when run together but fail in isolation or different order. See references/smell-examples.md for the SMELL/FIX pair (each test creating its own preconditions).
Review action: Request data isolation. Each test must create its own preconditions.
External Service Coupling
What it looks like: Tests call real external APIs (payment gateways, email providers, third-party services). See references/smell-examples.md for the SMELL/FIX pair (mocking the service boundary).
Review action: Request mock or fake at the service boundary. External calls belong in integration/contract tests, not unit tests.
Diagnostic Smells
Problems that make test failures hard to understand and debug.
Weak Assertion Messages
What it looks like: Assertion fails with no context about what was expected or why. See references/smell-examples.md for the SMELL/FIX pair (replacing toBe(true) with specific assertions like expect(result.errors).toEqual([]) that surface the offending value).
Review action: Request stronger assertions with diagnostic value. The failure message should explain the problem without reading the test source.
Multiple Failure Causes Per Test
What it looks like: A single test covers multiple independent behaviors. When it fails, you do not know which behavior broke. See references/smell-examples.md for the SMELL/FIX pair (splitting a lifecycle test into one-behavior-per-test).
Review action: Request test splitting. Each test should have one reason to fail.
Design Smells
Problems in test architecture that increase maintenance cost.
Conditional Test Logic
What it looks like: if/else, switch, ternaries, or for loops inside test bodies. Branching logic in a test is itself untested — you cannot tell which cases actually ran. See references/smell-examples.md for the SMELL/FIX pair (converting a branching loop into it.each).
Review action: Request parameterized tests (it.each / test.each). Conditional logic in tests hides which cases are actually verified.
Giant Fixtures
What it looks like: A beforeEach or fixture that sets up 20+ objects for every test, even though each test uses 2-3 of them. See references/smell-examples.md for the SMELL/FIX pair (replacing a monolithic beforeEach with per-test inline setup).
Review action: Request inline setup. Move shared setup to factories, not monolithic beforeEach blocks.
Over-Mocking
What it looks like: Every collaborator is mocked, including simple value objects and pure functions. See references/smell-examples.md for the SMELL/FIX pair (dropping a mock of the very function under test).
Review action: Request removal of unnecessary mocks. Mock boundaries, not internals.
AI-Generated Test Smells
When the test code came from a coding agent (Claude Code, Codex, Cursor, Copilot), the smell taxonomy is the same — but a few signature failures recur often enough to deserve their own pass.
| Smell | Detection |
|---|---|
| Hallucinated locator | Run the test against a real page once. If the locator never matches, the LLM invented a data-testid that doesn't exist. |
| Fabricated import | Static-check every imported symbol — does the file or package actually export it? LLMs invent plausible APIs (@testing-library/something-that-doesnt-exist). |
| Generic test data | example.com, test@test.com, Lorem ipsum, John Doe — boilerplate the agent generated because it had no project-specific factory. Replace with the project's data factory. |
| Closed AI loop | Both implementation and tests authored by the same agent in the same session. The tests just describe what the agent produced; they don't constrain it. Pair the agent's tests with at least one human-authored boundary test, or use TDD (test-first) per shift-left-testing. A low mutation score (see Verification) is the objective tell. |
| Project-convention drift | Page Object, fixture, naming, or assertion style different from the rest of the suite. AI-generated code rarely matches local conventions out of the box. |
For first-time test generation patterns and the Step-7 review checklist, cross-link ai-test-generation. For AI-system eval suites (the equivalent of ESLint for prompts), wire each tool's CLI runner — promptfoo eval, deepeval test run (Apache 2.0), Ragas ragas evaluate / experiments (Apache 2.0) — as quality gates parallel to your test runner.
Promptfoo ownership note: Promptfoo was acquired by OpenAI (announced 9 Mar 2026). The core stays MIT-licensed, open source, and model-agnostic; red-team capabilities are being folded into OpenAI Frontier.
promptfoo evalis still the correct quality-gate command — just expect the vendor to be OpenAI going forward.
Coverage Smells
Problems that leave gaps in what is verified.
Happy Path Only
What it looks like: Every test provides valid input and expects success. No error paths tested. See references/smell-examples.md for the SMELL/FIX pair (adding zero, max, negative, and boundary cases to a discount calculator).
Review action: Request missing scenarios. Use the BOUNDARY framework: Boundary values, Null/empty, Duplicates, Ordering, Range limits.
Missing Boundary Cases
What it looks like: Tests for "normal" values (5 items) but not for 0, 1, max, or max+1. Use it.each to cover boundaries explicitly: empty collection, single item, exact page size, one over, large set.
Review action: Request boundary tests. Every numeric parameter, string length, and collection size has boundaries to test.
Missing Error/Negative Cases
What it looks like: No tests for what happens when things go wrong — network failures, invalid input, permission denied, concurrent modification.
Review action: For each happy path test, ask: "What is the corresponding failure mode?" Request tests for the failure.
Testability Analysis
When reviewing application code, assess whether it is structured for testability. Each subsection has a hard-to-test vs. testable before/after in references/testability-refactors.md.
Dependency Injection
Flag classes that instantiate dependencies directly (new PostgresDatabase(), new StripeClient() inside methods). Suggest constructor injection so tests can substitute mocks/fakes. See references/testability-refactors.md.
Side Effect Isolation
Flag functions that mix pure calculation with I/O (email, logging, analytics). Extract the calculation as a pure function, then call it from the side-effectful orchestrator. See the calcTotal before/after in references/testability-refactors.md.
Pure Function Extraction
Look for validation, transformation, and business rules buried inside request handlers. If logic is inline in app.post('/api/orders', ...), it cannot be unit-tested without spinning up an HTTP server. Extract it as a standalone function. See the shippingFor before/after in references/testability-refactors.md.
Interface Segregation
Flag classes that depend on broad interfaces (entire PrismaClient) when they only use 2-3 methods. Suggest a narrow interface with only the methods actually used, making test doubles trivial to implement. See references/testability-refactors.md.
Review Workflow
PR Review Checklist
For each test file in a PR, check systematically:
## Test Quality Review
### Readability
- [ ] Can I understand what each test verifies in under 10 seconds?
- [ ] Is setup minimal and test-relevant?
- [ ] Are test names descriptive: "should [behavior] when [condition]"?
### Reliability
- [ ] No sleep/waitForTimeout/setTimeout for synchronization?
- [ ] No shared mutable state between tests?
- [ ] No dependency on test execution order?
- [ ] No calls to real external services?
### Diagnostic Value
- [ ] Will failures produce messages that identify the problem?
- [ ] Does each test have one reason to fail?
- [ ] Are assertions specific (not toBeTruthy/toBeDefined)?
### Design
- [ ] No conditional logic (if/else/switch/for) in test bodies?
- [ ] Fixtures/setup proportional to what each test needs?
- [ ] Mocking limited to external boundaries?
- [ ] Parameterized tests (it.each) used for data-driven scenarios?
### AI-Generated (if applicable)
- [ ] Locators verified against a real page (no hallucinated data-testid)?
- [ ] Imports resolve (no fabricated APIs)?
- [ ] Project data factory used, not test@test.com / John Doe?
### Coverage
- [ ] Happy path AND error/negative paths tested?
- [ ] Boundary values tested (0, 1, max, max+1)?
- [ ] Edge cases: empty, null, duplicate, concurrent?
Batch Audit Process
For a full test suite audit:
- Quantify: Count tests by type (unit/integration/E2E), framework, and directory.
- Sample: Review 10-20% of test files, prioritizing the largest and most recently changed.
- Pattern: Identify the 3-5 most common smells across the sample.
- Prioritize: Rank by impact: reliability smells > diagnostic smells > design smells > readability smells.
- Automate: For each common smell, determine if an ESLint rule or a mutation-score gate can catch it automatically.
- Report: Document findings (one row per file reviewed) with specific examples, suggested fixes, severity (high/medium/low), and estimated effort.
Prompt Templates
Three prompt patterns for AI-assisted review:
Review test quality: "Check this test file for readability, reliability, diagnostic, design, AI-generated, and coverage smells. For each issue: name the smell, cite the line, explain why it matters, and provide a fix."
Identify coverage gaps: "Given this application code and its existing tests, identify missing scenarios across happy path, error handling, boundaries, edge cases, concurrency, and security. Prioritize as P0/P1/P2."
Testability improvements: "Review this application code for hard-coded dependencies, mixed side effects, extractable pure functions, and overly broad interfaces. Show current vs. refactored code."
Anti-Patterns
Reviewing test code with production-code standards only. Test code has additional quality dimensions (reliability, diagnostics, coverage) that production-code linters do not check. Apply the six smell buckets, not just "clean code" principles.
Flagging every smell without context. A 50-line test for a complex state machine is not obscure setup — it is necessary complexity. Evaluate smells against the behavior being tested.
Suggesting mocks for everything. Over-mocking is itself a smell. Do not recommend mocking pure functions, value objects, or fast in-process collaborators. Mock boundaries: network, database, filesystem, clock.
Focusing on coverage percentage over coverage quality. 95% line coverage with only happy-path tests is worse than 75% coverage that includes error paths and boundaries. Review what is asserted, not just what is executed — and back it with mutation score.
Reviewing without running. Static analysis misses runtime issues. Run the suite (see Verification), check for flakiness with repeated runs, and check execution time. A passing suite that takes 20 minutes has a performance smell.
One-time review without follow-up. Test quality degrades over time. Establish a recurring review cadence or automated quality gates (lint rule, mutation threshold) that catch regression.
Verification
Run before you start commenting — these are the runtime checks the skill insists on, made concrete. Scope them to the PR's changed test files in PR review; run the whole suite in a batch audit.
- Run the suite once. Confirm it is green before reviewing — never review red or skipped tests as if they pass.
- Vitest:
npx vitest run <files>· Jest:npx jest <files>· Playwright:npx playwright test <files>· pytest:pytest <files>
- Vitest:
- Repeat to surface flakiness. A test that passes once and fails on the next run is the reliability smell, not a fluke.
- Vitest:
npx vitest run --retry=0 <files>looped, orfor i in 1 2 3; do npx vitest run <files> || break; done - Jest:
npx jest <files> && npx jest <files> && npx jest <files>(orjest-circusrepeat) - Playwright:
npx playwright test --repeat-each=3 <files> - pytest:
pytest --count=3 <files>(pytest-repeat) orpytest -p no:randomlyvs random order to catch order dependency
- Vitest:
- Capture per-test timing. A 20-minute suite has a performance smell.
- Vitest:
--reporter=verbose(prints per-test duration) · Jest:--verbose· Playwright:--reporter=list· pytest:--durations=10
- Vitest:
- Mutation score — the objective backstop. For the qualitative smells you can't eyeball at scale (Closed AI loop, weak assertions), run a mutation runner and read the score. AI-generated tests under ~60% mutation score are not constraining the implementation. Full tooling, thresholds, and config in
references/mutation-testing.md.- JS/TS:
npx stryker run· Java: PITmvn ... mutationCoverage· Rust:cargo mutants· Python:mutmut run
- JS/TS:
Output of steps 1-3 plus the mutation score is the evidence behind every "reliability"/"diagnostic" finding in the report.
Done When
- The findings artifact exists with one row per reviewed file, each row carrying a severity rating (high/medium/low). (file exists, row count == files reviewed)
- Every smell dimension that applies to the reviewed code is covered: readability, reliability, diagnostic, design, AI-generated, coverage. (six headings present in the report; "N/A" allowed, blank not)
- Each high-severity finding has an actionable remediation step (what + why + fix), not just a description.
- Verification ran: the suite executed at least 3x green (no flaky failures) and per-test timing captured; for AI-generated suites, a mutation score is recorded.
- At least one recurring smell was converted to an automated gate — an ESLint rule, a CI check, or a mutation-score threshold committed — or the report explicitly states none was warranted.
Reference Files (in references/)
- smell-examples.md — Full SMELL/FIX code for every catalogued smell across reliability, diagnostic, design, and coverage dimensions.
- testability-refactors.md — Hard-to-test vs. testable before/after for all four testability subsections: dependency injection, side effect isolation, pure function extraction, interface segregation.
- mutation-testing.md — Tooling (Stryker/PIT/cargo-mutants/mutmut), thresholds, Stryker config, and the AI-loop / weak-assertion gate.
Related Skills
- unit-testing — Framework-specific patterns (Jest, Vitest, pytest) that inform what "good" looks like for each framework.
- shift-left-testing — Pre-commit hooks and IDE integration that catch test smells before review.
- coverage-analysis — Interpreting coverage reports to find meaningful gaps, not just percentage targets.
- ai-test-generation — Generated tests need review too. Apply these smell checks to AI-generated test code.
- test-reliability — Reliability smells (sleep-based waits, order dependency) overlap with flaky test patterns.