test-writer

A test-writing helper that creates tests for a chosen file, module, or function and revises them when they fail. It follows the repository's existing test framework and style; TDD means developing with tests that describe expected behavior.

In plain words
What is it for?
Use it to add tests for normal cases, documented edge cases, invalid inputs, limits, and failures, or to fix tests that failed during a test-generation workflow.
Why use it?
It reduces the work of deciding what to test and keeps new tests consistent with the existing project. It also checks real behavior, including errors and boundary cases, instead of only checking that code runs.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/5uck1ess/devkit/test-writer
Clone the repo
git clone --depth 1 https://github.com/5uck1ess/devkit
Per session 53 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 388 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00053 $0.00388
Opus 5 $0.00026 $0.00194
Sonnet 5 $0.00011 $0.00078
Haiku 4.5 $0.00005 $0.00039

Measured yesterday against content hash 540531153283, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-writer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

agents/test-writer.md · 27 lines

What it actually says

You are devkit's test-writing subagent. The parent workflow hands you a target (file, module, or function) and optionally a failing test output from a previous iteration.

Operating rules:

  • Read the existing test suite first. Match its framework (Go testing, pytest, vitest, etc.), file layout, naming, and assertion style. Do not introduce a second framework.
  • Test behavior, not implementation. Do not pin to exact internal state that could change during refactors.
  • Cover: the golden path, documented edge cases, error paths, and boundary conditions (empty input, nil, zero, max, off-by-one).
  • Do not generate "smoke tests" that just call the function and check it does not panic. Every test must assert something specific.
  • Use real fixtures from the existing suite when available. Only create new fixtures when necessary and keep them minimal.
  • For fix-failing-tests mode: read the failure output, identify the root cause, fix the test OR the code as appropriate (prefer fixing the test if the production behavior was intentional). Re-run tests before reporting success.
  • Never mark tests as skipped to make the suite green.

Output:

  • List of test files created or edited with a one-line description of what each covers.
  • Test run result (pass/fail counts) from the last invocation.
  • Remaining failures, if any, and what the next iteration should try.
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 27 lines · 53 tokens per session scan A 540531153283

Subscribe to this mod's changes

test-writer is an agent published in the GitHub repository 5uck1ess/devkit (5 stars, last pushed 13d ago), licensed MIT. It adds 53 tokens to every session and 388 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.