A testnet is the dress rehearsal: the same rules, the same tooling, tokens worth nothing, so the mistakes cost nothing either. Every serious integration runs its webhook wiring, its confirmation policies, and its edge cases on testnet before touching mainnet money.
Testnets stay honest by being boring: faucets drip worthless tokens, resets happen, and nothing carries over. The discipline they enforce is the point, verify the flow end to end where failure is free.
Integration testing runs the checkout, webhook, and settlement flows against safe networks before a store goes live, the same paths, none of the stakes.
Every term behind the rails, the assets, and the settlement.