You might have different tests on your tests tab: some of them are from the Predefined Tests library, some were created by you or your colleagues. If you do not want to use some particular test anymore, or want to come back to it in the future, having it on the same list with actual tests could probably be disturbing.
With the 'Archive' button you will be able to hide the test and reactivate it later when you have recruitment for this position again in the future.
First you need to go to the 'Tests' tab and click on 'Your tests'.
Now, pick the tests and click on 'Archive' button. After this, the test will disappear from the list of your tests. However, remember that you can easily reactivate it.
To reactivate a test/see the archived tests you need to click on 'Show archived tests' button.
Find the test you want to reactivate and click on the 'Activate' button. Now this test will be available for you again.