How should I compose an integrated test for a service used across an application

Suppose I have the mediator service for communication with transferData and onDataTrasfered, methods that is used across the application by different services. Here is example of two services using the mediator: the Action service uses its transferData method and Renderer services uses its getTransferedData method. Here is the pseudocode:

// inside Renderer service
mediator.onDataTransfered(function() {});

// inside Action service
mediator.transferData(data);

My question is how should I write my integration test? Any examples with pseudocode are appreciated.