The standard uses message headers that a supporting mailbox application can act on. The visible unsubscribe link in the email body is a separate route. (Google email sender guidelines ↗ · RFC 8058: One-Click Unsubscribe)
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Testing the message header path
The publisher inspects a delivered test message for the List-Unsubscribe header fields used by the one-click mechanism, triggers the mailbox’s unsubscribe action, and verifies that the address is suppressed from a later eligible send. It tests the visible footer link separately; the two controls are not the same path.
The two headers have different jobs
List-Unsubscribe supplies the unsubscribe destination. List-Unsubscribe-Post tells a supporting mailbox that the message offers the one-click mechanism. Check the delivered message because an email provider can add or change headers after the template is prepared.
Confirm that the reader actually stops receiving the stream
Test with an address you control. Use the unsubscribe action, then verify how the mailing system records it and whether a later eligible campaign reaches that address. A working button and a durable suppression are separate outcomes.