In the second installment of a series on Elasticsearch testing and quality assurance processes, the article delves into the various testing layers employed to ensure software reliability. It highlights the importance of replicating test environments locally, mirroring those used in continuous integration setups to efficiently identify bugs. The text describes different testing levels, including unit tests for core algorithm validation, integration tests for Java API interactions with local Elasticsearch clusters, REST tests for endpoint verification, and backward compatibility tests to ensure seamless operation between different software versions. Additionally, the article discusses the use of declarative YAML-defined REST API tests and rigorous code quality checks embedded in the build process, such as identifying inefficient API usage and enforcing compatibility standards. It concludes by mentioning the importance of disabling broken tests during development and addressing them before release, with a preview of the upcoming focus on Elasticsearch's randomized testing framework.