openarc.org provides infrastructure you may use to get familar with ARC.
Send a message to email@example.com. You'll receive a response seconds later. This response contain the message as received by the service. This allowes you to inspect how OpenARC validate your sent message.
Send a message to firstname.lastname@example.org. You'll receive your message forwarded back to you seconds later. It's not a new one. Existing DKIM signatures are expected to be still intact after forwarding.
But you may force message modification to invalidate your existing DKIM signature: Choose the text "modify" as Subject and it will be prepended with "[MODIFIED]: " on forwarding. Your DKIM signature will be no longer valid. We assume you sign the RFC5322.Subject header as advised by RFC 6376 - DKIM Signatures