Also on 2019 on Android Dev Summit '19 said that we should ALWAYS inject Dispatchers to make the dis...

# coroutines

[Pablo]

Also on 2019 on Android Dev Summit '19 said that we should ALWAYS inject Dispatchers to make the dispatcher different from production as in the unit test. Is still like this?

[gildor]

it’s an opinion. It’s indeed good advice in general, but you pay for it by more complex set up and additional code

[Pablo]

Totally agree. If you don't inject, what do you do on Test?

[gildor]

what do you mean “what do you do on test”?

[gildor]

most of cases perfectly testable with any dispatcher

[gildor]

if api designed to be testable

[gildor]

but if you just have some class that launches some background job and doesn’t allow to await it somehow, you are in trouble, so have to inject test dispatcher instead

[gildor]

but also for cases if you need time advance feature, you have to use test dispatcher, so you also should somehow inject it to class, but it doesn’t required for all cases (“ALWAYS”)

[Pablo]

So if I inject the TestCoroutineScope and the TestcoroutineDispatcher i don't need to use the Dispatchers.setMain(TestCoroutineDispatcher()) and Dispatchers.resetMain() right? Because I'm setting it on my constructor

[gildor]

yes

[gildor]

and it’s the only option for other dispatchers

[Pablo]

I see, because I was creating a rule for testing, but then what you are saying to me now is that if I create this TestCoroutineScope and TestCoroutineDispatcher via constructor on my rule I don't need this

@Beforeall
fun setUp(){
Dispatchers.setMain(TestCoroutineDispatcher())
}

@afterEach
fun afterEach(){
testScope.cleanUpTestCoroutines()
}

@AfterAll
fun tearDown(){
Dispatchers.resetMain()
}

[Pablo]

Right?

[gildor]

you also can do testScope.context[CoroutineDispatcher]!!

[gildor]

to get dispatcher associated with scope

[gildor]

you shouldn’t create a new dispatcher every time

[Pablo]

But my question is, does it really need a Rule for this? If I'm injecting the CoroutineScope and the CoroutineDispatcher does it helps? No, right?
I mean, if I do inject, and in the test create the TestCoroutineScope and the TestCoroutineDispatcher and create the presenter on this case passing that as a parameter, I don't need anything else, right?
Or do I have to cleanUpTestCoroutines() in the tearDown ? What I mean is, I created the Rule but now that you've explained to me that Dispatchers.setMain(..) and Dispatchers.resetMain() doesn't change the IO it's not necessary to do it anymore, even if I'm creating the TestCoroutineDispatcher right?
So when creating the test I just need, create these TestCoroutineX and that's it?

[gildor]

rule is really useful to replace main dispatcher, if you inject it, I don’t see reason to have a rule and would just use runBlockingTest

[Pablo]

And last question, is it necessary to cleanupTestCoroutines() ?

[gildor]

This checks ensures that no coroutines are running on test scope (which may be a bug), runBlockingTest does this automatically after lambda is invoked

[Pablo]

Awesome, thanks Andrey 😉

[Pablo]

Have a good day!

[gildor]

Night 🛏️ 😄