What’s the best way to use Docker for integration testing in Java projects?

We've been using Testcontainers for our integration tests, especially since it integrates well with Spring. It's great for bringing up dependencies like databases on the fly. When I've had issues with startup times, I switched on reusable containers which helped a lot during development. For cleanup, I namespace test data, ensuring tests run independently without colliding. In terms of CI flakiness, we found it was a bit tricky since our CI pipelines are also dockerized, making us reconsider how we run our tests. Overall, Testcontainers is definitely a valuable part of our strategy, but it's slower compared to isolating tests.

We've had a mix of approaches. For our legacy apps with heavy databases, we sometimes rely on external infrastructure. When we can, Testcontainers is our go-to for spinning up dependencies during testing. I also look into GitHub Actions services for some situations, especially if they're a better match for customized Docker images. That way, we’re not depending entirely on Testcontainers, which is mainly good for standard setups. Just a reminder for those using Testcontainers: be sure to check the compatibility of your images, especially if you're working with newer architecture like M1 Macs.

I wrote a custom Gradle plugin that spins up Postgres and OpenSearch containers using Testcontainers for my integration tests. It’s been efficient, but I’ve noticed that H2 works well for most data needs if you prefer to mock external systems. Testcontainers is great, but I’ve hesitated to jump on the bandwagon for every scenario. Sometimes simplicity with mocks is just easier and faster.

In our projects, we mostly use Testcontainers since it simplifies handling external dependencies. However, I've encountered some hiccups, particularly with Postgresql and Kafka when using GitHub Actions. The images sometimes didn’t mesh well. For the tests to run smoothly, I make sure to manage migrations appropriately. Also, I’d recommend looking into using embedded databases for straightforward testing if you can avoid the complexities of containerized setups altogether.

Testcontainers are really popular these days because they automate the setup of the necessary containers. It’s a solid choice because you don’t typically have to worry about port conflicts, thanks to the random port assignment. However, I've noticed that it can slow down CI tasks since they run on VMs, not in containers, which adds to the startup time. That said, if you can optimize your CI setup to reuse containers, that can reduce the wait. Just be aware that tests that require this setup will generally take longer.