Ask HN: Which SaaS products provide test details / sandbox environments?

I'm trying to pull together a list of SaaS products which provide test details/sandbox environments i.e. - Payment details to simulate e-commerce transactions i.e. Stripe, GoCardless - A mobile number to simulate an SMS message being sent i.e. Nemxo, Twilio - An API key to provided access to a limited feature set for evaluation - A sandbox environment for full simulation of your integration. - A mailbox you can send an email to in order to check it's potential spam score. - etc Do any of you provide test details for your SaaS products or know of any SaaS products that do?