In my experience, payment processors (and related services) are somewhat unique in providing test gateways & APIs.
They are also somewhat unique in that they handle real money. You don't need a simulated API if you're sending an email or SMS message to a designated recipient or downloading the local weather forecast or traffic news, because there are no significant and irreversible consequences to these actions anyway.
They are also somewhat unique in that they handle real money. You don't need a simulated API if you're sending an email or SMS message to a designated recipient or downloading the local weather forecast or traffic news, because there are no significant and irreversible consequences to these actions anyway.