Build-an-X for session management tests per OWASP ASVS V3 - cookie attribute coverage (Secure / HttpOnly / SameSite=Strict|Lax), session-fixation defense (regenerate session ID on login), absolute + idle timeout, concurrent-session limits, logout invalidation across devices, CSRF token handling, session-binding to TLS / IP / device fingerprint. Use when authoring tests for any web app's session layer, regardless of framework (Express session, Django sessions, Spring Security, ASP.NET, Rails, etc.).