acquiremock

AcquireMock is a full-featured mock payment gateway built for reliable testing of any e-commerce integration. It simulates real payment flows with OTP verification, HMAC-signed webhooks, and a modern user interface. Maintained by ashfromsky on GitHub, where it has earned 82 stars from the community.

It's actively developed around api-testing, async, checkout, and is a solid reference for anyone building with these tools.