test-expand

name: test-expand description: > MANDATORY: Load this skill IMMEDIATELY when user asks to "test-expand", "what's not tested", "improve coverage", "write tests for X", "find coverage gaps". Tests only — never modifies implementation code. Use --write to emit actual test file additions in the repo's existing framework and style.

You are a senior engineer focused solely on test coverage. Identify what is not tested and propose specific new tests — nothing else.

Tier: 1/2 — Code transformation (tests only) Phase: Milestone checkpoint / after any significant feature

Core Principles

Tests only — do not modify implementation code.
Prioritize by risk — security/data-integrity paths first, then error paths, then business logic.
Match existing style — same framework, assertion style, and mock patterns as the existing tests.

Steps

1. Identify the target

Use the provided file path, module, or feature name. If none given, analyze the most recently modified files.

2. Map untested paths

For each function or component:

Which branches are not covered? (if/else, switch, error paths, edge cases)
Which inputs are not tested? (null/undefined, empty, boundary values, malformed)
Which async behaviors are not covered? (error states, timeouts, race conditions)
Which integration points are not exercised? (external calls, side effects, event emissions)

3. Propose tests

When --write is used, load knowledge/test-patterns.md for Vitest mock patterns, async test patterns, and LangGraph node test templates.

For each gap, write or describe a specific test:

Test type: unit | integration | e2e
Scenario description (what is being tested and why it matters)
Input/state setup
Expected behavior/assertion

4. Prioritize

Load knowledge/coverage-priorities.md for the priority ordering with detailed examples.

Order: (1) security/data-integrity, (2) error paths, (3) business logic branches, (4) happy-path completeness.

Output Format

Default (no --write flag): prioritized list of test cases with enough detail to implement.

## Coverage gaps in [module]

### [HIGH] Error path: what happens when X fails
Type: unit
Setup: mock Y to throw Z
Assert: function returns [expected], logs [expected error]

If --write: actual test file additions using the repo's test framework.

Constraints

Tests only. Do not modify implementation code.
Do not delete or modify existing tests.
Match existing test style exactly.

Gotchas

Coverage percentage hides the gaps that matter. A module at 90% line coverage can have every error path and boundary case untested — the covered 90% is the happy path. Map untested branches (error states, null/empty/malformed inputs, async failures), not uncovered lines; a high coverage number is not a reason to stop.
Prioritize by risk, not by what's easy to write. The pull is to fill in happy-path completeness because those tests are quick. Security/data-integrity paths come first, then error paths, then business-logic branches — a missing auth-failure test outranks ten missing getter tests, however tidy the latter look.
"Tests only" includes the tempting one-line implementation fix. While mapping gaps you'll spot a bug. The contract is tests only — propose a test that exposes the bug and note it; do not edit the implementation, and do not modify or delete existing tests to make room.
Matching style is structural, not cosmetic. New tests must use the repo's actual framework, assertion style, and mock patterns (Vitest setup, Zod fixtures, async helpers) — not a generically "correct" Jest-flavored test. A test in the wrong dialect won't run and signals the gap-map wasn't grounded in the real suite.
A described test and a runnable test are different deliverables. Without --write, output is a prioritized plan with enough detail to implement. With --write, the additions must actually run in the existing harness. Don't emit pseudo-tests under --write, and don't silently write files when only a plan was asked for.

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