1. A computer-implemented method, comprising: receiving, from a client, a client request for an application service; responding to the client request with a live response by causing the client request to be processed by a production engine to generate the live response; determining a first state of the production engine as a result of processing the client request to generate the live response; identifying, based on the received client request, one or more request processors to process the client request and a processing order, wherein the one or more request processors includes a shadow engine, which is a potential production engine being tested against live traffic without interfering with the production engine; causing the received client request to be processed via the shadow engine after responding to the client request with the live response; determining a second state of the shadow engine as a result of processing the client request; and identifying a difference between the states of the shadow engine and the production engine.