How to use the eventEmitter capability provided by service.once?

[andyloughran]

Summary

In your documentation, you cite the ability to use event emitters for helping with test instances. Unfortunately the documentation doesn't articulate how to set the 'service' variable.

Desired solution

Please provide an example for how to initialise the 'service' variable.

Additional Context

I think this is generic, but not sure if it needs guidance for specific test frameworks too.