Unsubscribe Links As well as Other Link Click rates do not work during a test email. This is with intention. It is setup this way to prevent you from running false positive unsubscribes or link clicks as a result hurting/burning a lead.
If you truly want to test the effectiveness of the unsubscribe, create a test email sequence, add one of your own email accounts as a lead. Send a test campaign, and you will see the unsubscribe link work well in an actual campaign.
The test email functionalities goal is to help you with verifying copy and formatting.