Please don’t test a Gmail forwarder by sending an email to yourself from the Gmail account that you are forwarding to. For example:
If I forward email from email@example.com to firstname.lastname@example.org, and I test this forwarder by sending an email to email@example.com from firstname.lastname@example.org, this will not appear in my inbox at email@example.com. Google conversation view doesn’t allow this to appear like any normal email, because you already have a copy of it in your Sent folder. Test the forwarder from a different email account that isn’t the one you are forwarding to.