Here are a few links which helped me to understand what to use to mock microservices with REST API. Just for a case, I've choosen wiremock because I need Java and saboteur functionality.
A summary on approaches for microservices testing: Working Locally with Microservices.
The presentation points to:
An easy way to start with WireMock is to workout the open-source wiremock workshop by Bas Dijkstra.
Finally, there are use cases: