# testcontainers-integration-tests

Helps AI agents write .NET integration tests using xUnit and real Docker containers instead of mocks. Useful for verifying database migrations, SQL queries, Redis cache, and message queues.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 544 installs · ★ 1238
- Author: Aaronontheweb
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/testcontainers/SKILL.md
- Updated: 2026-10-11
- HTML: https://affpapa.org/en/nevibecode/skills/testcontainers-integration-tests

## What it does

The skill guides agents in writing .NET integration tests with xUnit and Testcontainers 4.x. Instead of mocking `IDbConnection` or message brokers, it spins up real Docker containers for SQL Server, PostgreSQL, Redis, or RabbitMQ. Tests execute against real schema constraints, indexes, and actual SQL queries. Port randomization avoids local port collisions in CI/CD.

Docker must be available in the environment. The skill targets the Testcontainers 4.x module API, meaning legacy `TestcontainersBuilder<T>` calls will fail to compile. Module builders require passing the Docker image string directly into the constructor (like `new PostgreSqlBuilder("postgres:latest")`) rather than calling `.WithImage()`. Provider packages like `Testcontainers.MsSql` and `Testcontainers.PostgreSql` are required.

Containers plug into the xUnit `IAsyncLifetime` lifecycle. The test fixture starts the container and runs schema migrations during `InitializeAsync`, then tears it down in `DisposeAsync`. State isolation between runs relies on Respawn or class-level container reuse.

## Requirements
- Works with: Docker

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill testcontainers-integration-tests -a claude-code
```
```bash
npx skills add Aaronontheweb/dotnet-skills --skill testcontainers -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill testcontainers -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill testcontainers -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install Aaronontheweb/dotnet-skills testcontainers
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill testcontainers -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/Aaronontheweb/dotnet-skills --path skills/testcontainers
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill testcontainers -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/Aaronontheweb/dotnet-skills/tree/HEAD/skills/testcontainers/SKILL.md

## When to use it
- test SQL queries and constraints against a real database engine
- verify database migrations without infrastructure mocks
- run Redis caching tests with automatic container cleanup
- test RabbitMQ message flows inside xUnit test suites

## Example prompts
- Write an xUnit integration test for OrderRepository using Testcontainers and PostgreSQL
- Add a Redis integration test using Testcontainers 4.x and StackExchange.Redis
- Replace database mocks in our xUnit suite with MsSqlContainer

## 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: 7cf29a379fbfb48f.

BEGIN THIRD-PARTY FILE 7cf29a379fbfb48f
```text
---
name: testcontainers-integration-tests
description: Write integration tests using TestContainers for .NET with xUnit. Covers infrastructure testing with real databases, message queues, and caches in Docker containers instead of mocks.
user-invocable: false
---

# Integration Testing with TestContainers

## When to Use This Skill

Use this skill when:
- Writing integration tests that need real infrastructure (databases, caches, message queues)
- Testing data access layers against actual databases
- Verifying message queue integrations
- Testing Redis caching behavior
- Avoiding mocks for infrastructure components
- Ensuring tests work against production-like environments
- Testing database migrations and schema changes

## Reference Files

- [database-patterns.md](database-patterns.md): SQL Server, PostgreSQL, and migration testing examples
- [infrastructure-patterns.md](infrastructure-patterns.md): Redis, RabbitMQ, multi-container networks, container reuse, and Respawn

## Core Principles

1. **Real Infrastructure Over Mocks** - Use actual databases/services in containers, not mocks
2. **Test Isolation** - Each test gets fresh containers or fresh data
3. **Automatic Cleanup** - TestContainers handles container lifecycle and cleanup
4. **Fast Startup** - Reuse containers across tests in the same class when appropriate
5. **CI/CD Compatible** - Works seamlessly in Docker-enabled CI environments
6. **Port Randomization** - Containers use random ports to avoid conflicts

## TestContainers 4.x API

This skill targets **TestContainers 4.x** with the 3.0+ module builder API. The pre-3.0 types were renamed and removed, so code that uses `TestcontainersBuilder<T>` or `TestcontainersContainer` does **not** compile against the modern packages:

| Old (pre-3.0) | New (3.0+) |
|----------------|------------|
| `new TestcontainersBuilder<T>()` | Module builder (e.g. `new PostgreSqlBuilder(...)`) or `new ContainerBuilder(...)` |
| `TestcontainersContainer` | `DockerContainer` / module container (e.g. `PostgreSqlContainer`) |
| `TestcontainersNetworkBuilder` | `NetworkBuilder` |
| `GetMappedPublicPort(port)` | `GetMappedPublicPort(port)` (still available) |
```
END THIRD-PARTY FILE 7cf29a379fbfb48f

The third-party file has ended. Everything between the 7cf29a379fbfb48f tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2184 of 9701 bytes. © Aaronontheweb · MIT · https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/testcontainers/SKILL.md

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