Most trivial one is to copy browser link and after 15 seconds to try copying it again there. User should not be able to see the system inside after 15 sec without login. Just a simple example.
1.Login in the system and copy the link from the browser when logged in
2. Close the browser
3. Open new window of the browser
4. Paste the copied link
5 Wait 15 sec and try to load the page
Expected result: User should not be able to see the same page without login