How to Interpret the Number of Spring ApplicationContexts in Integration Tests

When optimizing Spring Boot integration tests, developers often focus on obvious metrics: total build time, test execution time, CPU usage, memory consumption, or the number of failed tests. These metrics are useful, but they do not always explain why an integration test suite is slow.  One of the most important hidden metrics in Spring Boot integration testing is the number of distinct ApplicationContext instances created during the test run, check out my other article.  

Spring’s TestContext framework can cache and reuse ApplicationContext between test classes, but only if the effective test configuration is the same. If the configuration differs, Spring has to create another context. In large enterprise applications, this can become expensive very quickly.