You can find the RFA Java Warm Standby detail in section 13.14 Warm Standby of the RFA Java Developer Guide document. You can download RFA Java Developer Guide document from this link.
The API package also contains the StarterProvider_WarmStandby example that illustrates the Warm Standby feature. You can test it with the RFA Java StarterConsumer example and the configurations shows in the picture below.
rmdstestcelint is a test client that connects to a single infrastructure host and subscribes. It's designed for testing various types and versions of infrastructure for connectivity and to examine data content.
Unless one specifically re-points rmdstestclient to a different host, it is not aware of any other hosts, then the one it was configured to connect to on startup.
Therefore, I do not see how it can be used in testing a custom RFA implementation of warm standby.