Closing idle sessions helps manage server resources and ensures session data security by terminating inactive sessions.
Idle sessions will not be automatically closed. The user sessions will remain open until they are explicitly closed or until the server is restarted.
Set Set closeIdleSession=true in https://git.magnolia-cms.com/projects/PLATFORM/repos/ce/browse/magnolia-empty-webapp/src/main/webapp/WEB-INF/web.xml#45
Make sure the setting in empty webapp is either inherited or duplicated in other webapps (including test webapps) such as DX core webapp.