When you view your courses under your curriculum you may see an orange bookmark tab next to each course. Hover over it and you will see a message "Jump to my last working page". Click on the orange book mark and it will do just that.
When you view all the modules in a course you will also see something similar.
This all means you can start and stop your courses anytime and you can always go back to exactly the last working page.
Similarly for the tests. You can stop a test in the middle ... logout then log back in at a later time and the test is there ready for you to continue from where you last left off.