How to rostest multiple nodes (C++) (python)

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Hello, My goal is to use rostests to test whether individual nodes communicate with each other. I have a control-module node that subscribe the topic from the gps-module and camera-module and then publish the data to the topic for the motors. The question is: What do I need to make rostests and how are they used and built? How can I use them and do I need to build another rostest node or simply just build a launch file in a particular node that subscribe and publish from other nodes. I would like to use publishtests to check if the node sends at least one time a topic and paramtests because we use the Param Server.