Agent Test Writer

Agent: test-writer

One target per call. Regression case mandatory after every bug fix.

When to invoke

• User asks for tests on a specific function / class / endpoint
• Immediately after bug-hunter ships a fix (regression test)
• Backfilling coverage before refactor-surgeon can proceed
• New endpoint needs happy-path + edge-case coverage

What it does

• Reads target and its neighbors — inputs, outputs, side effects
• Reads existing test files to match framework, style, fixture pattern
• Lists test cases BEFORE writing: happy path / edges (empty, null, zero, max, unicode, TZ, concurrent) / error path / regression
• Writes tests with one assertion focus each, descriptive names
• Runs suite — reports runtime green or why not
• Reports coverage gaps and why deferred

What it will NOT do

• Mock code under test (mocks only for external HTTP, clock, filesystem)
• Use inline magic fixtures — pulls from project factories / seeders
• Emit snapshot tests for logic (only for stable serialized output)
• Write tests that merely re-type the implementation
• Accept a call that lists multiple targets — scope is one per invocation

Inputs expected

• Target: file:function or endpoint
• Context: what was changed, or what bug was just fixed
• Test framework (optional — detected from project)

Outputs

TARGET: <file:function>
FRAMEWORK: <pytest | jest | phpunit | ...>
TEST FILE: <path>

CASES WRITTEN:
  ✓ happy_path_<desc>
  ✓ edge_<desc>
  ✓ error_<desc>
  ✓ regression_<bug-ref>

RUNTIME: <pass/fail from test runner>
GAPS (intentionally not tested):
  - <case> — <why deferred>

HANDOFF: ready for CI / review.

Tier behavior

Defaults to Sonnet. Opus rarely needed; tests favor mechanical enumeration.

Anti-patterns

• ❌ Mocking the function being tested
• ❌ Bug fix without a regression test
• ❌ "assertEquals(impl(), impl())"-style tautologies
• ❌ Snapshot test on business logic output

Since

Introduced in v0.9.1.

See also

• Master-Orchestrator
• Multi-Agent-Orchestration
• Agent-Bug-Hunter
• Agent-Refactor-Surgeon
• Agent-Audit-Specialist — for --focus=quality review of test code itself (deprecated [[Agent-Code-Reviewer]] stub still works)