Simon Willison’s Weblog


Testcontainers (via) Not sure how I missed this: Testcontainers is a family of testing libraries (for Python, Go, JavaScript, Ruby, Rust and a bunch more) that make it trivial to spin up a service such as PostgreSQL or Redis in a container for the duration of your tests and then spin it back down again.

The Python example code is delightful:

redis = DockerContainer(“redis:5.0.3-alpine”).with_exposed_ports(6379)
wait_for_logs(redis, “Ready to accept connections”)

I much prefer integration-style tests over unit tests, and I like to make sure any of my projects that depend on PostgreSQL or similar can run their tests against a real running instance. I’ve invested heavily in spinning up Varnish or Elasticsearch ephemeral instances in the past—Testcontainers look like they could save me a lot of time.

The open source project started in 2015, span off a company called AtomicJar in 2021 and was acquired by Docker in December 2023.