# tdd

Guides a strict red-green-refactor cycle for .NET 10 applications using xUnit v3, WebApplicationFactory, and Testcontainers.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 2800 installs · ★ 789
- Author: codewithmukesh
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/codewithmukesh/dotnet-claude-kit/tree/HEAD/skills/tdd/SKILL.md
- Updated: 2026-08-07
- HTML: https://affpapa.org/en/nevibecode/skills/codewithmukesh-tdd

## What it does

The skill enforces a test-driven workflow across .NET projects. Instead of adding tests after writing features, it writes a failing test first. Once the test fails as expected, the agent writes the minimal implementation to pass it, then refactors using modern C# patterns.

Integration tests rely on `WebApplicationFactory` and real databases like PostgreSQL or SQL Server inside `Testcontainers`. Assertions stick to standard xUnit `Assert` methods. This avoids licensing friction because FluentAssertions requires a commercial license starting from version 8.

Complex features get broken down into sequential cycles where each step handles a single behavior. For trivial config changes or raw documentation, skipping this workflow makes sense.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill tdd -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/tdd/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/tdd/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill tdd -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/tdd/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill tdd -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/tdd/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install codewithmukesh/dotnet-claude-kit tdd
```

2. **Manually: put the files in place**
- File: `.github/skills/tdd/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill tdd -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/codewithmukesh/dotnet-claude-kit --path skills/tdd
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/tdd/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add codewithmukesh/dotnet-claude-kit --skill tdd -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/codewithmukesh/dotnet-claude-kit/tree/HEAD/skills/tdd/SKILL.md

## When to use it
- define API behavior with a failing integration test first
- reproduce a bug with a test before fixing the source code
- break multi-step feature development into discrete cycles
- spin up PostgreSQL or SQL Server via Testcontainers for integration tests

## Example prompts
- /tdd Let's TDD a product search endpoint
- /tdd create an order management feature with acceptance criteria
- /tdd reproduce and fix the empty cart validation bug

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: b4785d188a84352f.

BEGIN THIRD-PARTY FILE b4785d188a84352f
````text
---
name: tdd
description: >
  Guided test-driven development workflow for .NET 10 using xUnit v3,
  WebApplicationFactory, Testcontainers, and Verify snapshots. Follows the
  strict red-green-refactor cycle. Use when: "TDD", "test-driven", "let's TDD
  this", "red green refactor", "write the test first", or when building a
  feature with clear acceptance criteria.
---

# /tdd -- Red-Green-Refactor for .NET

## What

Guides a strict test-driven development cycle for .NET features. Instead of
writing implementation first and bolting on tests after, this command flips the
order: write a failing test that defines the desired behavior, implement the
minimum code to make it pass, then refactor with confidence.

Every cycle uses the .NET testing stack:
- **xUnit v3** -- Test framework with `[Fact]` and `[Theory]`
- **WebApplicationFactory** -- Integration tests against the real HTTP pipeline
- **Testcontainers** -- Real databases (PostgreSQL, SQL Server) in tests
- **Verify** -- Snapshot testing for complex response structures
- **FakeTimeProvider** -- Deterministic time in tests

## When

- User says "TDD", "test-driven", "let's TDD this", "write the test first"
- Building a new feature with clear acceptance criteria
- Fixing a bug (write a test that reproduces the bug first, then fix)
- Adding behavior to an existing feature (test the new behavior first)
- Any time the user wants proof that code works before it ships

**Skip TDD for:** Trivial config changes, scaffolding without logic, documentation.

## How

### Cycle: Red -> Green -> Refactor

Each feature goes through one or more TDD cycles. A cycle covers one discrete behavior.

#### Step 1: Red -- Write the Failing Test

Write a test that describes the desired behavior. The test MUST fail because the
implementation does not exist yet.

```csharp
[Fact]
public async Task CreateOrder_WithValidItems_Returns201WithOrderId()
{
    // Arrange
    var client = _factory.CreateClient();
    var request = new CreateOrderRequest([
        new OrderItemRequest("SKU-001", 2, 29.99m)
    ]);

    // Act
    var response = await client.PostAsJsonAsync("/api/orders", request);

    // Assert — plain xUnit Assert (FluentAssertions v8+ requires a commercial license)
    Assert.Equal(HttpStatusCode.Created, response.StatusCode);
    var result = await response.Content.ReadFromJsonAsync<CreateOrderResponse>();
    Assert.NotNull(result);
    Assert.NotEqual(Guid.Empty, result.OrderId);
}
```

Run the test and confirm it fails:
```bash
dotnet test --filter "CreateOrder_WithValidItems_Returns201WithOrderId"
```

If the test passes without implementation, the test is not testing what you think.
Rewrite it.

#### Step 2: Green -- Minimal Implementation

Write the minimum code to make the test pass. Do not add features, optimizations,
or edge case handling. The goal is a green test, nothing more.

- Create the endpoint, handler, request/response types, and EF config as needed
- Use the simplest logic that satisfies the test assertion
- Do not refactor yet -- ugly passing code is fine at this stage

Run the test and confirm it passes:
```bash
````
END THIRD-PARTY FILE b4785d188a84352f

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First 3126 of 5526 bytes. © codewithmukesh · MIT · https://github.com/codewithmukesh/dotnet-claude-kit/tree/HEAD/skills/tdd/SKILL.md

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