testing

testing is a skill for Claude Code, Codex from krzysztofsurdy/code-virtuoso. It costs 103 tokens per session (2,628 once invoked), scanned A, original, MIT.

A general guide to checking that software behaves correctly and stays reliable as it changes. It covers unit tests for small pieces, integration tests for connected parts, end-to-end tests for whole user flows, test doubles, and TDD—writing a test before the code it describes.

In plain words
What is it for?
Use it to design a test strategy, review existing tests, choose between unit, integration, and end-to-end testing, apply TDD, and investigate flaky tests.
Why use it?
It helps choose the right kind of test and avoid suites that are slow, fragile, or unhelpful. Good tests also document expected behaviour and make refactoring safer.

Skill for Claude CodeCodex

Part of the knowledge-virtuoso plugin — 15 skills 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 skills/krzysztofsurdy/code-virtuoso/testing
Any agent
npx skills add krzysztofsurdy/code-virtuoso --skill testing
Clone the repo
git clone --depth 1 https://github.com/krzysztofsurdy/code-virtuoso

Made for: Claude Code, Codex.

Or install knowledge-virtuoso, the plugin that ships this one along with the rest of its 15 skills.

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 testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/krzysztofsurdy/code-virtuoso/testing.svg)](https://agentmods.dev/skills/krzysztofsurdy/code-virtuoso/testing)
Your own site
<a href="https://agentmods.dev/skills/krzysztofsurdy/code-virtuoso/testing"><img src="https://agentmods.dev/badge/skills/krzysztofsurdy/code-virtuoso/testing.svg" alt="Measured on agentmods" height="20"></a>
Per session 103 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,628 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 $0.00103 $0.02628
Opus 5 $0.00051 $0.01314
Sonnet 5 $0.00021 $0.00526
Haiku 4.5 $0.00010 $0.00263

Measured 4d ago against content hash 904a18106822, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

testing 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 4d 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.

skills/knowledge/testing/SKILL.md · 276 lines

How it starts

The opening of the file, as written. The whole thing — 276 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Testing

A disciplined approach to verifying that software behaves correctly, remains stable under change, and communicates intent to future developers. Good tests act as living documentation, a safety net for refactoring, and a design feedback mechanism.

This skill covers universal testing concepts that apply regardless of language, framework, or tooling.

When to Use

  • Designing a test strategy for a new project or feature
  • Deciding what level of testing (unit, integration, e2e) a piece of code needs
  • Evaluating whether existing tests are providing value or creating drag
  • Applying TDD to drive design decisions
  • Debugging a flaky or brittle test suite
  • Reviewing test code for quality and maintainability

Testing Pyramid

The testing pyramid describes the ideal distribution of tests across three levels. More tests at the base, fewer at the top.

        /  E2E  \           Few, slow, expensive
       /----------\
      / Integration \       Moderate number, moderate speed
     /----------------\
    /    Unit Tests     \   Many, fast, cheap
   /____________________\

Unit Tests (Base)

  • Test a single unit of behavior in isolation (a function, a method, a small class)
  • No I/O, no database, no network, no file system
  • Execute in milliseconds
  • Should form the majority of your test suite (roughly 70%)
  • Fast feedback loop enables rapid iteration

Integration Tests (Middle)

  • Test how multiple units collaborate, or how code interacts with external systems
  • May involve a real database, message queue, or HTTP endpoint
  • Execute in seconds
  • Verify that wiring, configuration, and contracts between components work
  • Roughly 20% of your test suite

End-to-End Tests (Top)

  • Test complete user journeys through the full system
  • Interact with the application as a user would
  • Slowest, most brittle, most expensive to maintain
  • Reserve for critical business paths only
  • Roughly 10% of your test suite

The Ice Cream Cone Antipattern

The inverted pyramid: many e2e tests, few unit tests. Symptoms:

Read the full file on GitHub · 276 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 4d ago First seen · 276 lines · 103 tokens per session scan A 904a18106822

Subscribe to this mod's changes

testing is a skill published in the GitHub repository krzysztofsurdy/code-virtuoso (20 stars, last pushed 3mo ago), licensed MIT. It adds 103 tokens to every session and 2,628 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.

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