Playwright storageState is not just a setup file. It is a contract.

The text discusses the challenges and solutions associated with managing authentication states in Playwright, a popular testing framework. It highlights how a shared authentication file, used to store login state across multiple tests, can lead to test failures when a logout test inadvertently overwrites this state, causing subsequent tests to fail by being redirected to the login page. To address this issue, the text suggests a three-rule approach: utilizing per-test storage paths to prevent shared file overwrites, running tests that alter session states in isolated contexts, and implementing code review checks to ensure only authorized scripts can modify the shared authentication file. Additionally, it touches on the necessity of validating session states for long-running authentication scenarios and how tools like Mergify can help identify the source of test failures by tracking the sequence of test runs. The document emphasizes the importance of scoping shared resources to prevent similar issues and improve test reliability.