I believe product agility is a huge asset early on, and I think testing cuts into this. I disagree that testing cuts into agility. I believe that in this case

I believe product agility is a huge asset early on, and I think testing cuts into this. I disagree that testing cuts into agility. I believe that in this case "agility" means that you can change your product in significant ways quickly. Presumably, when you make these changes, you need it to still work. Having tests already in existence will inform you when you've broken something you didn't mean to change. If you don't have tests that can run frequently on your swiftly changing, rapidly pivoting codebase, you will break things and you won't even know until it takes off someone's foot. If you don't have these tests, you can't rapidly change your product with confidence that it still works, and I suspect that you would value "working" above "not working" very very highly. If you want agility, you need tests. Lots of automated tests. Testing doesn't cut into your agility; testing gives you agility.