Improving Elixir Test Suites with Asynchronous Testing

The article discusses the importance of maintaining a healthy test suite in Elixir, emphasizing speed and reliability. It argues that the main causes of slow and flaky tests can often be addressed with robust asynchronous testing strategies. The author explains how asynchronous tests facilitate handling side effects and the challenges posed by singletons during testing. Practical examples illustrate the issues, particularly with GenServers and Logger, and discuss solutions for overcoming these obstacles. Additionally, the concept of resource ownership is presented, where each test process can own its resources, thus allowing for more isolated and parallel execution of tests. The use of ProcessTree and nimble_ownership libraries for better management of test scenarios is also explored, along with strategies to effectively reduce singleton usages and leverage mocks where appropriate. Through these practices, the article aims to empower developers to create more efficient and reliable testing frameworks in their Elixir applications.