If enabled on your account you will be able to watch a video recording of a candidate's test. This will show you all of the keystrokes and where they have clicked on the page.
It is possible to go through it section by section and analyse the test in great detail. To access the recording, click on the candidate and then the test invite. You will then see a button that says 'Show screen recording'
If you have a test that lasts a considerable amount of time and the candidate was to leave and come back, this will have no effect on the recording as the system will on record when there is activity.