Testing
MailHog is an open-source local SMTP server that captures all outgoing emails and exposes them via a web UI and HTTP API. No signups, no internet connection required, and no risk of emails reaching real users. This guide covers running MailHog in Docker, asserting on captured emails via its HTTP
Chaos Engineering
Pumba is a chaos testing tool for Docker containers. It kills containers, pauses them, and injects network failures using Linux tc (traffic control) — directly on your Docker host or inside Docker Compose environments. If you run microservices locally with Docker Compose or test in Docker-based CI environments, Pumba is the
Security Testing
Trivy is an open-source vulnerability scanner that covers container images (OS packages and application dependencies), Kubernetes manifests, Terraform, Dockerfiles, and secrets. It's fast, requires no setup beyond installation, and produces structured JSON or table output. Use Trivy in CI to block builds with critical vulnerabilities before they reach
Testing
Shipping a container image without testing it is like deploying code without running tests. The image might contain known CVEs in its base layer, misconfigured file permissions, unnecessary packages that expand your attack surface, or missing dependencies that cause runtime failures. All of these are detectable before the image ever
Integration Testing
Mocking database calls in Python tests creates a false sense of security. testcontainers-python spins up real PostgreSQL, Redis, and MongoDB containers via Docker during your pytest run, giving you genuine integration coverage without managing external services. Key Takeaways testcontainers-python integrates with pytest through fixtures. Define containers in conftest.py and
Testing
Mocks lie. They model your assumptions about a dependency, not the dependency itself. When a PostgreSQL query behaves differently across versions, when a Redis EXPIRE command has subtle timing behavior, or when Kafka consumer group rebalancing breaks your processing logic — mocks won't catch it. Testcontainers will. Testcontainers is
Integration Testing
Node.js integration tests that mock PostgreSQL and Redis test your assumptions, not your code. testcontainers starts real database containers during your Jest run and tears them down after. Your tests talk to the actual services — no mocks, no drift, no surprises. Key Takeaways testcontainers/node works with Jest, Vitest,
Testing
Shared test databases are a shared pain. Developer A's test inserts rows that Developer B's test finds and misinterprets. A parallel CI run leaves the database in an unexpected state. Someone runs a cleanup migration and breaks the next six test runs. Docker Compose eliminates this
Docker
Shipping a Docker image without testing it is like deploying code without tests — the problems show up in production. Docker containers need their own testing layer: build tests, container smoke tests, integration tests, and security scans. Here's how to build that layer. Key Takeaways Test at four levels:
CI/CD
Container-based integration tests are slower in CI than you want them to be — mostly because of image pulls, layer rebuilds, and serial test execution. Fix that with layer caching, GitHub Actions service containers, and parallel job splitting. Here's exactly how. Key Takeaways GitHub Actions service containers are the