Complex/long-running tests fill up the guest machine's allocated space. When Virtual Machine hosting the browser or device running your tests has run out of space on its virtual disk. This causes the browser to crash, which ends your test.

This isn't always restricted to the tests, either; an app under test which consumes a large amount of memory, which suffers from significant JS memory leaks or which opens a lot of tabs can cause this issue.

Best practice to avoid this is to clear cookies when started a Test, also to close unnecessary tabs that are not being used. 

 NLP to clear cookies: 

                                                 1. Delete all cookies from the current session

                                          2. Delete all local storage cookies from the current session

NLP to close tabs:

                                   1. Close all windows except the current window

                                   2. Close the window that has title test data

                                   3. Close the window with index test data