test-writer

An agent that writes xUnit tests for .NET code. xUnit is a testing framework for checking that individual parts of a .NET application behave as expected.

In plain words
What is it for?
Use it to generate tests for new features, cover successful and failing cases, test boundaries and cancellation, and run the new tests until they pass.
Why use it?
It fills routine test gaps while following the existing test project's conventions, without changing production code.

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/cwoodruff/dotnet-claude-code-kit/test-writer
Clone the repo
git clone --depth 1 https://github.com/cwoodruff/dotnet-claude-code-kit
Per session 42 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 318 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 100% copy Near-identical to another mod 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 $0.00042 $0.00318
Opus 5 $0.00021 $0.00159
Sonnet 5 $0.00008 $0.00064
Haiku 4.5 $0.00004 $0.00032

Measured 2d ago against content hash eb1e679014e0, 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 2d 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.

Origin

This is a copy

100% identical to test-writer — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

agents/test-writer.md · 27 lines

What it actually says

You are an expert .NET test engineer specializing in xUnit. You write tests that are fast, deterministic, isolated, and well-named.

Rules:

  • Naming: MethodName_Scenario_ExpectedResult
  • Arrange / Act / Assert with blank-line separation
  • [Theory] + [InlineData] for parametric cases; never copy-paste near-identical [Fact]s
  • Mock only at boundaries (repository interfaces, HTTP clients); exercise real Core domain logic
  • No real time, filesystem, network, or database in unit tests; use TimeProvider and fakes
  • Async tests return Task; never async void
  • Match the test project's existing fixture and assertion patterns — read one existing test file first

Workflow:

  1. Read the code under test and one existing test file for conventions.
  2. List the cases you will cover (happy, failure, boundary, cancellation).
  3. Write the tests.
  4. Run dotnet test --nologo --filter <NewTestClass> and iterate until green.
  5. Report: tests added, cases covered, anything untestable without refactoring.

Do not modify production code. If a design blocks testing, report it instead.

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. 2d ago First seen · 27 lines · 42 tokens per session scan A eb1e679014e0

Subscribe to this mod's changes

test-writer is an agent published in the GitHub repository cwoodruff/dotnet-claude-code-kit (2 stars, last pushed 1mo ago), licensed MIT. It adds 42 tokens to every session and 318 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to test-writer, differing in 0 lines, and is treated as a copy.