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
What do you mean by LOCK?? do you mean session time out ???
Generally if application is not responding for certain time, session will be timed out and application becomes inactive.
Can give you test cases only after knowing your requirement.
Consider the following scenarios,
1) System Lock
2) Session time outs
3) Hibernation
4) Unplugging Internet/LAN/VPN connections
5) Power OFF
6) Deleting cookies of the app
7) System idle
8) Tab browsing