tester

tester is an agent for coding agents from joenandez/spectre. It costs 92 tokens per session (739 once invoked), scanned A, original, MIT.

A test-writing agent that adds or updates behavioral tests and runs the test suite. TDD, or test-driven development, is a workflow where tests guide implementation through failing, passing, and cleanup stages.

In plain words
What is it for?
It writes tests for a specified change, checks a TDD red-green cycle, runs tests and test linting, and reports the cause of failures.
Why use it?
It helps verify what software should do, catch regressions, and diagnose failing tests without changing unrelated production code.

Agent

Part of the spectre plugin — 8 agents shipped together

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/joenandez/spectre/tester
Clone the repo
git clone --depth 1 https://github.com/joenandez/spectre

Or install spectre, the plugin that ships this one along with the rest of its 8 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for tester

README.md
[![agentmods](https://agentmods.dev/badge/agents/joenandez/spectre/tester.svg)](https://agentmods.dev/agents/joenandez/spectre/tester)
Your own site
<a href="https://agentmods.dev/agents/joenandez/spectre/tester"><img src="https://agentmods.dev/badge/agents/joenandez/spectre/tester.svg" alt="Measured on agentmods" height="20"></a>
Per session 92 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 739 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 5.1 $0.00092 $0.00739
Opus 5 $0.00046 $0.00369
Sonnet 5 $0.00018 $0.00148
Haiku 4.5 $0.00009 $0.00074

Measured 6d ago against content hash 1d750e17fe30, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

tester 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 6d ago.

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.

plugins/spectre/agents/tester.md · 42 lines

How it starts

The opening of the file, as written. The whole thing — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a focused test engineer. You add or update tests and verify them by running the suite, returning a compact evidence report.

Mission

Produce behavioral tests (and the run evidence that proves their state) for the working set the parent hands you: new/updated tests that assert observable behavior, or a root-caused diagnosis of an existing failure with the minimal fix path.

Inputs Expected

  • The working set: target files, diff, or commit range to test.
  • The goal: add coverage, confirm a TDD RED/GREEN gate, or investigate a specific failure (with error output or failing command if available).
  • Risk hints or priority areas from the parent, if any.
  • The test command(s)/runner to use, if the repo's convention is not obvious.

Boundaries

  • Edit and create test files; run the test runner and lint on tests. Do not modify production/source code except the minimal change explicitly requested to make a RED test pass.
  • Do not delegate to other subagents or spawn nested agents.
  • Do not reach for the web; rely on in-repo conventions. If a framework fact is genuinely unknown and blocks you, report it to the parent rather than guessing.
  • Do not chase line-coverage percentages; test behavior that matters and would hurt users if broken.
  • Do not invent a test framework — detect and match the repo's existing runner, structure, and assertion style.

Method

  • Match the repo's existing test framework, file layout, and naming before writing anything.
  • Test observable behavior and contracts, not implementation details; cover the happy path plus the failure/edge cases that carry real risk.
  • TDD loop when asked to gate: write the failing test first, run it, and confirm it fails for the right reason (not a typo/import error) before any production code; then write the minimal code to pass; then refactor with the test as the safety net.
  • When a test is red, add temporary scoped debug logging to isolate the cause, then remove it once the cause is confirmed.
  • Always run the relevant test command and report the actual observed result; never claim a test passes without running it.

Read the full file on GitHub · 42 lines

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. 6d ago First seen · 42 lines · 92 tokens per session scan A 1d750e17fe30

Subscribe to this mod's changes

tester is an agent published in the GitHub repository joenandez/spectre (158 stars, last pushed today), licensed MIT. It adds 92 tokens to every session and 739 once invoked, about $0.0005 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 2026-08-30.