How do you test coroutines started with `launch` If I unders

Question

How do you test coroutines started with `launch` If I understand correctly `launch` always run asynchronously and in tests we would like to run it sequentially

Allan Wang · Answer

wrap it with `runBlocking` then use ` join `

gumil · Answer

What if the call to `launch` is abstracted I don t have access to the `job`

ghedeon · Answer

is join required iiric `runBlocking` is enough Plus you need to override Main dispatcher on Android

Allan Wang · Answer

run blocking might be enough It might wait for all child launches to run so you have to ensure the scopes are used properly

gumil · Answer

hmm so does `runBlocking joinAll ` work too

Allan Wang · Answer

I think it s provided that the scope has a job and everything you are waiting on are children of that job Easiest way may be to just try

Dico · Answer

Yeah parent job cannot complete until the children completed so `parent join ` should join all `launch` is not always asynchronous it depends on the coroutine context

gumil · Answer

the problem I had was `launch` is abstracted so I am not able to get the `job` I had to wrap it in an `async` block and `await ` until everything is finished Do you guys know a cleaner way to do this

Dico · Answer

`coroutineContext Job `

Dico · Answer

No I don t really get what you re talking about

Dico · Answer

It s confusing and ambiguous

Dico · Answer

But the above is available in any suspend function or lambda

gumil · Answer

``` fun main args Array lt String gt = runBlocking abstractedCallToLaunch which I cannot get the job of the call to launch println this should execute after call to launch fun CoroutineScope abstractedCallToLaunch launch delay 1000 println do something ```

gumil · Answer

it s something like this and it prints ``` this should execute after call to launch do something ``` but it should be the other way around

Dico · Answer

It s like that because of the dispatcher provided by `runBlocking` which is an event loop on the blocked thread

Dico · Answer

You could try `coroutineContext Job joinChildren `

Dico · Answer

I think that exists after your abstracted launch

Dico · Answer

Or just `yield ` should work too but it might not wait for full completion

ghedeon · Answer

I feel like you expect something like `RxAndroidPlugins InstantTaskExecutorRule` but it s not coming <https github com Kotlin kotlinx coroutines issues 102> Basically your `launch` has a dispatcher attached so it s considered your responsibility to inject the right dispatcher in your test so the execution becomes synchronous

gumil · Answer

Yep something like it I m passing a dispatcher but `launch` always run asynchronously I m not sure how to make it run synchronously

ghedeon · Answer

Hm what about as simple as <https pl kotl in r1F5BarQE>

ghedeon · Answer

Basically ``` fun test blah blah runBlocking foo bar lt launch inside assert ```

Dico · Answer

Or `coroutineScope foo bar `