Testcontainers Integration Tests

Overview

Use real infrastructure in containers for integration tests. Mocks don't catch SQL bugs or database-specific issues. Testcontainers provides isolated, repeatable tests with production-equivalent infrastructure.

REQUIRED: superpowers:test-driven-development, superpowers:verification-before-completion

When to Use

•Integration tests need real database, queue, or cache
•Tests verify database-specific features (JSON, arrays, transactions)
•Mocking infrastructure is insufficient for test confidence
•Tests are flaky due to shared test database state
•Repository uses or should use Testcontainers

Detection and Deference

Before creating new Testcontainers setup, check for existing patterns:

bash

# Check for existing Testcontainers packages (.NET)
grep -r "Testcontainers" **/*.csproj 2>/dev/null

# Check for existing test fixtures
find . -name "*Fixture*.cs" -path "*/Tests/*" 2>/dev/null

# Check for existing container configurations
grep -r "PostgreSqlBuilder\|RedisBuilder\|RabbitMqBuilder" **/*.cs 2>/dev/null

If existing setup found:

•Use the existing fixture patterns and naming conventions
•Add new containers to existing collection definitions
•Follow established test isolation approach

If no setup found:

•Create shared fixtures using templates
•Document testing approach in docs/testing-strategy.md

Decision Capture

Document your integration testing approach:

markdown

<!-- docs/testing-strategy.md or docs/adr/NNNN-integration-testing.md -->

## Integration Testing Approach

**Decision:** Use Testcontainers for integration tests

**Containers Used:**

- PostgreSQL 15 - Primary database
- Redis 7 - Caching layer

**Rationale:**

- Real database catches SQL-specific issues
- Container isolation prevents test pollution
- CI/CD compatible with Docker support

**Lifecycle:**

- Shared fixtures per test collection (performance)
- Transaction rollback for test isolation

Core Workflow

•Identify infrastructure (database type, version, queue, cache)
•Select Testcontainers library (Java, .NET, Python, Node)
•Configure container with production-matching version
•Define lifecycle (per-class or shared fixture)
•Implement isolation (transactions, cleanup, fresh schema)
•Set up schema (migrations or scripts)
•Write tests against real infrastructure
•Optimize for CI (reuse, parallel, image pre-pull)

See references/language-setup.md for language-specific configuration. See references/performance-optimization.md for container reuse strategies. See references/ci-cd-integration.md for CI/CD patterns.

Quick Reference

Container	Use Case	Image
PostgreSQL	Relational DB	postgres:15
MySQL	Relational DB	mysql:8
MongoDB	Document DB	mongo:6
Redis	Cache	redis:7-alpine
RabbitMQ	Message Queue	rabbitmq:3.12-management
Kafka	Event Streaming	confluentinc/cp-kafka:7.4

Red Flags - STOP

•"Mocks are faster" / "H2 is close enough"
•"Shared test database is fine" / "CI doesn't support Docker"
•"Testcontainers is too slow" / "Just add better cleanup"

All mean: Apply testcontainers-integration-tests with optimizations.

See references/performance-optimization.md for rationalizations table.

Reference Templates

Test fixtures and project templates for quick setup:

Template	Purpose
postgres-fixture.cs	PostgreSQL shared fixture with xUnit
redis-fixture.cs	Redis shared fixture with xUnit
test-project.csproj	Test project with Testcontainers packages

Quick Setup

bash

# Copy test project template
cp templates/test-project.csproj.template tests/YourProject.Tests/YourProject.Tests.csproj

# Copy fixture templates
cp templates/postgres-fixture.cs.template tests/YourProject.Tests/Fixtures/PostgresFixture.cs
cp templates/redis-fixture.cs.template tests/YourProject.Tests/Fixtures/RedisFixture.cs

# Restore packages
dotnet restore tests/YourProject.Tests/

Container Packages

Install the appropriate Testcontainers package for your infrastructure:

bash

# PostgreSQL
dotnet add package Testcontainers.PostgreSql

# Redis
dotnet add package Testcontainers.Redis

# RabbitMQ
dotnet add package Testcontainers.RabbitMq

# MongoDB
dotnet add package Testcontainers.MongoDb

Sample CI Run Logs

Successful Test Run

text

Starting test execution...
[Testcontainers] Connected to Docker:
  Host: unix:///var/run/docker.sock
  Server Version: 24.0.7
  API Version: 1.43

[Testcontainers] Pulling image: postgres:15
[Testcontainers] Pulling image: redis:7-alpine
[Testcontainers] Creating container for image: postgres:15
[Testcontainers] Container 8a3f2b... created (postgres:15)
[Testcontainers] Starting container 8a3f2b...
[Testcontainers] Waiting for container 8a3f2b to be ready...
[Testcontainers] Container 8a3f2b started and ready (took 2.3s)
[Testcontainers] Creating container for image: redis:7-alpine
[Testcontainers] Container 4c7e91... created (redis:7-alpine)
[Testcontainers] Starting container 4c7e91...
[Testcontainers] Container 4c7e91 started and ready (took 0.8s)

Test run for MyApp.SystemTest.dll (.NETCoreApp,Version=v8.0)
Microsoft (R) Test Execution Command Line Tool Version 17.8.0

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.

Passed!  - Failed:     0, Passed:    47, Skipped:     0, Total:    47, Duration: 12.4 s

[Testcontainers] Stopping container 8a3f2b...
[Testcontainers] Container 8a3f2b stopped
[Testcontainers] Stopping container 4c7e91...
[Testcontainers] Container 4c7e91 stopped

Failed Test Run (Connection Issue)

text

Starting test execution...
[Testcontainers] Connected to Docker:
  Host: unix:///var/run/docker.sock

[Testcontainers] Creating container for image: postgres:15
[Testcontainers] Container 2d8a4f... created (postgres:15)
[Testcontainers] Starting container 2d8a4f...
[Testcontainers] Waiting for container 2d8a4f to be ready...
[Testcontainers] Container 2d8a4f started and ready (took 2.1s)

Test run for MyApp.SystemTest.dll (.NETCoreApp,Version=v8.0)

Starting test execution, please wait...

[xUnit.net 00:00:03.45]     MyApp.SystemTest.OrderTests.CreateOrder_WithValidData_ReturnsCreated [FAIL]
  Failed MyApp.SystemTest.OrderTests.CreateOrder_WithValidData_ReturnsCreated [1.2s]
  Error Message:
   Npgsql.NpgsqlException : Failed to connect to 127.0.0.1:32789
   ---> System.Net.Sockets.SocketException : Connection refused
  Stack Trace:
     at Npgsql.Internal.NpgsqlConnector.Connect(...)
     at MyApp.SystemTest.OrderTests.CreateOrder_WithValidData_ReturnsCreated() in OrderTests.cs:line 45

Failed!  - Failed:     1, Passed:    46, Skipped:     0, Total:    47, Duration: 8.7 s

[Testcontainers] Stopping container 2d8a4f...

CI Pipeline Output (GitHub Actions)

text

Run dotnet test tests/MyApp.SystemTest/
  dotnet test tests/MyApp.SystemTest/ --logger "console;verbosity=detailed" --collect:"XPlat Code Coverage"

info: Testcontainers[0]
      Docker container 8a3f2b is starting (image: postgres:15)
info: Testcontainers[0]
      Docker container 8a3f2b is ready (postgres:15)
info: Testcontainers[0]
      Docker container 4c7e91 is starting (image: redis:7-alpine)
info: Testcontainers[0]
      Docker container 4c7e91 is ready (redis:7-alpine)

Test Run Successful.
Total tests: 47
     Passed: 47
 Total time: 15.234 Seconds

Code Coverage Results:
  Generating report 'coverage.cobertura.xml'
  Line coverage: 78.5%
  Branch coverage: 72.3%

Container Lifecycle Checklist

Pre-Test Setup

• Docker daemon running and accessible
• Required images available (or network access to pull)
• Sufficient disk space for container volumes
• Port range available (Testcontainers uses random ports)
• Test database migration scripts ready

Per-Test Class Lifecycle

text

[Collection Start]
  │
  ├─► Create fixture (IAsyncLifetime.InitializeAsync)
  │     ├─► Pull image (if not cached)
  │     ├─► Create container
  │     ├─► Start container
  │     ├─► Wait for ready (health check)
  │     └─► Run migrations/seed data
  │
  ├─► Run tests (parallel within collection)
  │     ├─► Test 1: Begin transaction → Execute → Rollback
  │     ├─► Test 2: Begin transaction → Execute → Rollback
  │     └─► Test N: Begin transaction → Execute → Rollback
  │
  └─► Dispose fixture (IAsyncLifetime.DisposeAsync)
        ├─► Stop container
        └─► Remove container
[Collection End]

Test Isolation Checklist

• Each test runs in its own transaction (rolled back after)
• No shared mutable state between tests
• Test data created with unique identifiers
• Parallel tests don't conflict on resources
• Container state reset between test collections

CI Environment Checklist

• Docker-in-Docker or Docker socket mounted
• Sufficient memory for containers (min 2GB recommended)
• Container cleanup on job failure (use finally or always)
• Image caching configured for faster runs
• Timeout configured for container startup

Troubleshooting Checklist

Symptom	Check	Fix
Container won't start	Docker daemon running?	`docker ps` to verify
Connection refused	Using mapped port?	Use `container.GetMappedPublicPort()`
Tests timeout	Container ready check?	Add explicit wait strategy
Flaky tests	Transaction isolation?	Ensure rollback after each test
Slow CI	Image caching?	Pre-pull images in CI setup
Port conflicts	Random ports?	Let Testcontainers assign ports

Container Health Verification

csharp

// PostgreSQL ready check
public async Task WaitForPostgresReady()
{
    var connectionString = _postgres.GetConnectionString();
    await using var connection = new NpgsqlConnection(connectionString);

    var retries = 10;
    while (retries > 0)
    {
        try
        {
            await connection.OpenAsync();
            await using var cmd = new NpgsqlCommand("SELECT 1", connection);
            await cmd.ExecuteScalarAsync();
            return; // Ready
        }
        catch
        {
            retries--;
            await Task.Delay(500);
        }
    }
    throw new Exception("PostgreSQL container failed to become ready");
}

Evidence Template

markdown

## Integration Test Evidence

**Date**: YYYY-MM-DD
**Commit**: abc1234
**CI Run**: [link to CI job]

### Container Configuration

| Container  | Image          | Startup Time | Port  |
| ---------- | -------------- | ------------ | ----- |
| PostgreSQL | postgres:15    | 2.3s         | 32789 |
| Redis      | redis:7-alpine | 0.8s         | 32790 |

### Test Results

| Suite      | Total | Passed | Failed | Duration |
| ---------- | ----- | ------ | ------ | -------- |
| SystemTest | 47    | 47     | 0      | 12.4s    |

### Isolation Verification

- [x] Transaction rollback confirmed
- [x] No cross-test data leakage
- [x] Parallel execution stable

### Container Cleanup

- [x] All containers stopped
- [x] All containers removed
- [x] No orphaned volumes