Attached is a sanitized version of a solution realized for a customer at some point.
The presentation tries to describe what exactly was done.
The how was a custom implementation but it was at heart no rocket science and everyone that knows how to build a test case in DevTest can build himself such an executable contract engine. It is basically a testcase that opens a VSI file - which in itself is XML - and processed all the transactions defined in that VSI file. Each transaction becomes a testcase for the consumer of the contract fired against the System Under Test