I've done this a couple times in the past for projects where I owned the back-end and the front-end was outsourced. I documented the API spec, mocked the API t

I've done this a couple times in the past for projects where I owned the back-end and the front-end was outsourced. I documented the API spec, mocked the API to return hard-coded values, and wrote tests to cover the expected test cases. It was a bit of work up front, but it made the eventual integration almost seamless. In this case, I manually created the endpoints and mocked return values. If I did it again, I'd probably use something more automated like some of the other posters have mentioned.