# Test Coverage Audit (Step 3.4)

100% coverage is the goal — every untested path is a path where bugs hide and vibe coding becomes yolo coding. Evaluate what was ACTUALLY coded (from the diff), not what was planned.

## Contents

- [Test Framework Detection](#test-framework-detection)
  - [E2E Test Decision Matrix](#e2e-test-decision-matrix)
  - [REGRESSION RULE (mandatory)](#regression-rule-mandatory)
  - [Test Plan Artifact](#test-plan-artifact)
- [Affected Pages/Routes](#affected-pagesroutes)
- [Key Interactions to Verify](#key-interactions-to-verify)
- [Edge Cases](#edge-cases)
- [Critical Paths](#critical-paths)


## Test Framework Detection

Before analyzing coverage, detect the project's test framework:

1. **Read CLAUDE.md** — look for a `## Testing` section with test command and framework name. If found, use that as the authoritative source.
2. **If CLAUDE.md has no testing section, auto-detect:**

```bash
# Detect project runtime
[ -f Gemfile ] && echo "RUNTIME:ruby"
[ -f package.json ] && echo "RUNTIME:node"
[ -f requirements.txt ] || [ -f pyproject.toml ] && echo "RUNTIME:python"
[ -f go.mod ] && echo "RUNTIME:go"
[ -f Cargo.toml ] && echo "RUNTIME:rust"
# Check for existing test infrastructure
ls jest.config.* vitest.config.* playwright.config.* cypress.config.* .rspec pytest.ini phpunit.xml 2>/dev/null
ls -d test/ tests/ spec/ __tests__/ cypress/ e2e/ 2>/dev/null
```

3. **If no framework detected:** falls through to the Test Framework Bootstrap step (Step 2.5) which handles full setup.

**0. Before/after test count:**

```bash
# Count test files before any generation
find . -name '*.test.*' -o -name '*.spec.*' -o -name '*_test.*' -o -name '*_spec.*' | grep -v node_modules | wc -l
```

Store this number for the PR body.

**1. Trace every codepath changed** using `git diff origin/<base>...HEAD`:

Read every changed file. For each one, trace how data flows through the code — don't just list functions, actually follow the execution:

1. **Read the diff.** For each changed file, read the full file (not just the diff hunk) to understand context.
2. **Trace data flow.** Starting from each entry point (route handler, exported function, event listener, component render), follow the data through every branch:
   - Where does input come from? (request params, props, database, API call)
   - What transforms it? (validation, mapping, computation)
   - Where does it go? (database write, API response, rendered output, side effect)
   - What can go wrong at each step? (null/undefined, invalid input, network failure, empty collection)
3. **Diagram the execution.** For each changed file, draw an ASCII diagram showing:
   - Every function/method that was added or modified
   - Every conditional branch (if/else, switch, ternary, guard clause, early return)
   - Every error path (try/catch, rescue, error boundary, fallback)
   - Every call to another function (trace into it — does IT have untested branches?)
   - Every edge: what happens with null input? Empty array? Invalid type?

This is the critical step — you're building a map of every line of code that can execute differently based on input. Every branch in this diagram needs a test.

**2. Map user flows, interactions, and error states:**

Code coverage isn't enough — you need to cover how real users interact with the changed code. For each changed feature, think through:

- **User flows:** What sequence of actions does a user take that touches this code? Map the full journey (e.g., "user clicks 'Pay' → form validates → API call → success/failure screen"). Each step in the journey needs a test.
- **Interaction edge cases:** What happens when the user does something unexpected?
  - Double-click/rapid resubmit
  - Navigate away mid-operation (back button, close tab, click another link)
  - Submit with stale data (page sat open for 30 minutes, session expired)
  - Slow connection (API takes 10 seconds — what does the user see?)
  - Concurrent actions (two tabs, same form)
- **Error states the user can see:** For every error the code handles, what does the user actually experience?
  - Is there a clear error message or a silent failure?
  - Can the user recover (retry, go back, fix input) or are they stuck?
  - What happens with no network? With a 500 from the API? With invalid data from the server?
- **Empty/zero/boundary states:** What does the UI show with zero results? With 10,000 results? With a single character input? With maximum-length input?

Add these to your diagram alongside the code branches. A user flow with no test is just as much a gap as an untested if/else.

**3. Check each branch against existing tests:**

Go through your diagram branch by branch — both code paths AND user flows. For each one, search for a test that exercises it:
- Function `processPayment()` → look for `billing.test.ts`, `billing.spec.ts`, `test/billing_test.rb`
- An if/else → look for tests covering BOTH the true AND false path
- An error handler → look for a test that triggers that specific error condition
- A call to `helperFn()` that has its own branches → those branches need tests too
- A user flow → look for an integration or E2E test that walks through the journey
- An interaction edge case → look for a test that simulates the unexpected action

Quality scoring rubric:
- ★★★  Tests behavior with edge cases AND error paths
- ★★   Tests correct behavior, happy path only
- ★    Smoke test / existence check / trivial assertion (e.g., "it renders", "it doesn't throw")

### E2E Test Decision Matrix

When checking each branch, also determine whether a unit test or E2E/integration test is the right tool:

**RECOMMEND E2E (mark as [→E2E] in the diagram):**
- Common user flow spanning 3+ components/services (e.g., signup → verify email → first login)
- Integration point where mocking hides real failures (e.g., API → queue → worker → DB)
- Auth/payment/data-destruction flows — too important to trust unit tests alone

**RECOMMEND EVAL (mark as [→EVAL] in the diagram):**
- Critical LLM call that needs a quality eval (e.g., prompt change → test output still meets quality bar)
- Changes to prompt templates, system instructions, or tool definitions

**STICK WITH UNIT TESTS:**
- Pure function with clear inputs/outputs
- Internal helper with no side effects
- Edge case of a single function (null input, empty array)
- Obscure/rare flow that isn't customer-facing

### REGRESSION RULE (mandatory)

**IRON RULE:** When the coverage audit identifies a REGRESSION — code that previously worked but the diff broke — a regression test is written immediately. No AskUserQuestion. No skipping. Regressions are the highest-priority test because they prove something broke.

A regression is when:
- The diff modifies existing behavior (not new code)
- The existing test suite (if any) doesn't cover the changed path
- The change introduces a new failure mode for existing callers

When uncertain whether a change is a regression, err on the side of writing the test.

Format: commit as `test: regression test for {what broke}`

**4. Output ASCII coverage diagram:**

Include BOTH code paths and user flows in the same diagram. Mark E2E-worthy and eval-worthy paths:

```
CODE PATH COVERAGE
===========================
[+] src/services/billing.ts
    │
    ├── processPayment()
    │   ├── [★★★ TESTED] Happy path + card declined + timeout — billing.test.ts:42
    │   ├── [GAP]         Network timeout — NO TEST
    │   └── [GAP]         Invalid currency — NO TEST
    │
    └── refundPayment()
        ├── [★★  TESTED] Full refund — billing.test.ts:89
        └── [★   TESTED] Partial refund (checks non-throw only) — billing.test.ts:101

USER FLOW COVERAGE
===========================
[+] Payment checkout flow
    │
    ├── [★★★ TESTED] Complete purchase — checkout.e2e.ts:15
    ├── [GAP] [→E2E] Double-click submit — needs E2E, not just unit
    ├── [GAP]         Navigate away during payment — unit test sufficient
    └── [★   TESTED]  Form validation errors (checks render only) — checkout.test.ts:40

[+] Error states
    │
    ├── [★★  TESTED] Card declined message — billing.test.ts:58
    ├── [GAP]         Network timeout UX (what does user see?) — NO TEST
    └── [GAP]         Empty cart submission — NO TEST

[+] LLM integration
    │
    └── [GAP] [→EVAL] Prompt template change — needs eval test

─────────────────────────────────
COVERAGE: 5/13 paths tested (38%)
  Code paths: 3/5 (60%)
  User flows: 2/8 (25%)
QUALITY:  ★★★: 2  ★★: 2  ★: 1
GAPS: 8 paths need tests (2 need E2E, 1 needs eval)
─────────────────────────────────
```

**Fast path:** All paths covered → "Step 3.4: All new code paths have test coverage ✓" Continue.

**5. Generate tests for uncovered paths:**

If test framework detected (or bootstrapped in Step 2.5):
- Prioritize error handlers and edge cases first (happy paths are more likely already tested)
- Read 2-3 existing test files to match conventions exactly
- Generate unit tests. Mock all external dependencies (DB, API, Redis).
- For paths marked [→E2E]: generate integration/E2E tests using the project's E2E framework (Playwright, Cypress, Capybara, etc.)
- For paths marked [→EVAL]: generate eval tests using the project's eval framework, or flag for manual eval if none exists
- Write tests that exercise the specific uncovered path with real assertions
- Run each test. Passes → commit as `test: coverage for {feature}`
- Fails → fix once. Still fails → revert, note gap in diagram.

Caps: 30 code paths max, 20 tests generated max (code + user flow combined), 2-min per-test exploration cap.

If no test framework AND user declined bootstrap → diagram only, no generation. Note: "Test generation skipped — no test framework configured."

**Diff is test-only changes:** Skip Step 3.4 entirely: "No new application code paths to audit."

**6. After-count and coverage summary:**

```bash
# Count test files after generation
find . -name '*.test.*' -o -name '*.spec.*' -o -name '*_test.*' -o -name '*_spec.*' | grep -v node_modules | wc -l
```

For PR body: `Tests: {before} → {after} (+{delta} new)`
Coverage line: `Test Coverage Audit: N new code paths. M covered (X%). K tests generated, J committed.`

### Test Plan Artifact

After producing the coverage diagram, write a test plan artifact so `/mk:qa` can consume it:

```bash
eval "$(.claude/scripts/bin/workflow-slug 2>/dev/null)" && mkdir -p .claude/memory/projects
USER=$(whoami)
DATETIME=$(date +%Y%m%d-%H%M%S)
```

Write to `.claude/memory/projects/{slug}/{user}-{branch}-ship-test-plan-{datetime}.md`:

```markdown
# Test Plan
Generated by /mk:ship on {date}
Branch: {branch}
Repo: {owner/repo}

## Affected Pages/Routes
- {URL path} — {what to test and why}

## Key Interactions to Verify
- {interaction description} on {page}

## Edge Cases
- {edge case} on {page}

## Critical Paths
- {end-to-end flow that must work}
```