In the testing documentation: https://github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-test It's recommended to pass the scope through the constructor:

class Subject(val scope: CoroutineScope) {
    fun foo() {
        scope.launch {
            // launch uses the testScope injected in setup
        }
    }
}

But what do I actually pass in production code here?

It depends.... If you're an Android dev and this is part of your ViewModel, it would be a

MainScope()

or a

viewModelScope

. Or you create one on your own:

CoroutineScope(Job() + <http://Dispatchers.IO|Dispatchers.IO>)

for example