What tests, if any, should I carry out to test email designs prior to going live?

I’m designing a set of emails meant to warn the user to take action before an irreversible change will take place, and, for those users who didn’t take the action in time, to let them know that the irreversible change has taken place. It’s the first time I’m designing emails and was wondering whether there are any tests I could carry out to try and predict how well my emails would do in getting users to click on that one CTA I want them to click.

I’ve been Googling away but all I could really find is recommendations for a/b testing. I’m just wondering whether there are any kinds of tests people here use before going live with emails.

Here’s what I’ve been thinking so far:

• 5 second test to test gut reaction and layout.
• Thinking out loud / reading comprehension test: show wireframes to users and probe to find out whether the content is clear.

Am I missing anything? Am I actually going overboard and a/b testing should be enough? Would appreciate your thoughts.

Thanks