Using Testcontainters with Kotlin Spring Boot App

In this quick post I will show you how to use Testcontainers with Kotlin Spring Boot app. Testcontainers is a Java library that you can use to write integration tests that work with real third-party services like databases, message queues like Kafka, or any other service that can be packaged as a Docker container image.

Most developers use in-memory databases or fakes to test with external dependencies but to test against real stack you need to use real services. This week I faced as issue where one of my test was failing because a MySQL function was unavailable in H2. I was using in-memory H2 database in tests. My application used MySQL in the production mode. So, my valid MySQL query was not working when run in a test. This made me think of replacing H2 with MySQL database for tests.

I was aware of Testcontainers but had never used it in any application. So, this was the first time I used it. For most parts I liked it. I don’t have to work around limitations of H2 and I can hope I will not discover any issues because of difference between H2 and MySQL. Testcontainers is not perfect. It makes test slow. My build time has increased from 6 mins to 9 mins just because of Testcontainers. I am relying more on my CI server to run the complete test suite.

Testcontainers can do much more than running databases. You can use Testcontainers for:

  • Stream processing solutions like Apache Kafka and Apache Pulsar
  • AWS Localstack
  • Selenium tests
  • Chaos tests
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