Managing Environment Variables in Elixir Tests

The article shares the author's experience with flaky tests in an Elixir project, emphasizing the challenges of modifying environment variables during testing. Initially, the author encountered intermittent test failures when using `Application.put_env/4`, which led to unexpected configurations being returned. After testing various approaches, including adjusting the async settings, the author discovered that another test was modifying the same configuration in a way that caused data loss. The solution involved refactoring the conflicting function to ensure the entire configuration was correctly restored after tests, which resolved the flaky behavior. The key takeaway is to carefully manage environment variable modifications during tests to prevent cross-test pollution.