gstack/ship/sections/test-coverage.md

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## Step 7: Test Coverage Audit

**Dispatch this step as a subagent** using the Agent tool with `subagent_type: "general-purpose"`. The subagent runs the coverage audit in a fresh context window — the parent only sees the conclusion, not intermediate file reads. This is context-rot defense.

**Subagent prompt:** Pass the following instructions to the subagent, with `<base>` substituted with the base branch:

> You are running a ship-workflow test coverage audit. Run `git diff <base>...HEAD` as needed. Do not commit or push — report only.
>
> 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.

### 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
setopt +o nomatch 2>/dev/null || true  # zsh compat
# 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 4) 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 PATHS                                            USER FLOWS
[+] src/services/billing.ts                           [+] Payment checkout
  ├── processPayment()                                  ├── [★★★ TESTED] Complete purchase — checkout.e2e.ts:15
  │   ├── [★★★ TESTED] happy + declined + timeout      ├── [GAP] [→E2E] Double-click submit
  │   ├── [GAP]         Network timeout                 └── [GAP]        Navigate away mid-payment
  │   └── [GAP]         Invalid currency
  └── refundPayment()                                 [+] Error states
      ├── [★★  TESTED] Full refund — :89                ├── [★★  TESTED] Card declined message
      └── [★   TESTED] Partial (non-throw only) — :101  └── [GAP]        Network timeout UX

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 (2 E2E, 1 eval)
```

Legend: ★★★ behavior + edge + error  |  ★★ happy path  |  ★ smoke check
[→E2E] = needs integration test  |  [→EVAL] = needs LLM eval

**Fast path:** All paths covered → "Step 7: All new code paths have test coverage ✓" Continue.

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

If test framework detected (or bootstrapped in Step 4):
- 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 7 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.`

**7. Coverage gate:**

Before proceeding, check CLAUDE.md for a `## Test Coverage` section with `Minimum:` and `Target:` fields. If found, use those percentages. Otherwise use defaults: Minimum = 60%, Target = 80%.

Using the coverage percentage from the diagram in substep 4 (the `COVERAGE: X/Y (Z%)` line):

- **>= target:** Pass. "Coverage gate: PASS ({X}%)." Continue.
- **>= minimum, < target:** Use AskUserQuestion:
  - "AI-assessed coverage is {X}%. {N} code paths are untested. Target is {target}%."
  - RECOMMENDATION: Choose A because untested code paths are where production bugs hide.
  - Options:
    A) Generate more tests for remaining gaps (recommended)
    B) Ship anyway — I accept the coverage risk
    C) These paths don't need tests — mark as intentionally uncovered
  - If A: Loop back to substep 5 (generate tests) targeting the remaining gaps. After second pass, if still below target, present AskUserQuestion again with updated numbers. Maximum 2 generation passes total.
  - If B: Continue. Include in PR body: "Coverage gate: {X}% — user accepted risk."
  - If C: Continue. Include in PR body: "Coverage gate: {X}% — {N} paths intentionally uncovered."

- **< minimum:** Use AskUserQuestion:
  - "AI-assessed coverage is critically low ({X}%). {N} of {M} code paths have no tests. Minimum threshold is {minimum}%."
  - RECOMMENDATION: Choose A because less than {minimum}% means more code is untested than tested.
  - Options:
    A) Generate tests for remaining gaps (recommended)
    B) Override — ship with low coverage (I understand the risk)
  - If A: Loop back to substep 5. Maximum 2 passes. If still below minimum after 2 passes, present the override choice again.
  - If B: Continue. Include in PR body: "Coverage gate: OVERRIDDEN at {X}%."

**Coverage percentage undetermined:** If the coverage diagram doesn't produce a clear numeric percentage (ambiguous output, parse error), **skip the gate** with: "Coverage gate: could not determine percentage — skipping." Do not default to 0% or block.

**Test-only diffs:** Skip the gate (same as the existing fast-path).

**100% coverage:** "Coverage gate: PASS (100%)." Continue.

### Test Plan Artifact

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

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

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

```markdown
# Test Plan
Generated by /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}
```
>
> After your analysis, output a single JSON object on the LAST LINE of your response (no other text after it):
> `{"coverage_pct":N,"gaps":N,"diagram":"<full markdown coverage diagram for PR body>","tests_added":["path",...]}`

**Parent processing:**

1. Read the subagent's final output. Parse the LAST line as JSON.
2. Store `coverage_pct` (for Step 20 metrics), `gaps` (user summary), `tests_added` (for the commit).
3. Embed `diagram` verbatim in the PR body's `## Test Coverage` section (Step 19).
4. Print a one-line summary: `Coverage: {coverage_pct}%, {gaps} gaps. {tests_added.length} tests added.`

**If the subagent fails, times out, or returns invalid JSON:** Fall back to running the audit inline in the parent. Do not block /ship on subagent failure — partial results are better than none.

---