Tethys created due to the demand for testing the behavior of rest client when interacting with the server side. Basically it is smart mock server that enables the developer to setup a sequences of expected HTTP request that would be sent to the REST server and the corrosponding HTTP responses Tethys would send back. When HTTP request reach the server, Tethys compares the incoming request's data to the expected value and return the required response.

REST defines 2 main streams of client-server interaction;

• Client initiates HTTP request calls directed to the server (and recieves answer in the form of HTTP response)
• Server send notification (via websocket) to client. Client recieves this notifications in async manner.

Tethys creates mock server instance that simulates the rest server of your system, examines the incoming requests and sends back the required responses.