So yes, I tried and code inside `async` only runs ...

# coroutines

[aaverin]

So yes, I tried and code inside async only runs when I call await

[Martin Devillers]

async isnt’ lazy, but it is… asynchronous (shocker). So if you check immediately after calling your registerDevice whether the registerDeviceForService method has been called on lib, then it likely won’t be the case. A new thread is spawned, so you have to wait for the method to be called on that thread.

[Martin Devillers]

I don’t know how you’re injecting the lib mock into your instance, but in any case, you need to find a mechanism to suspend until `lib`’s method has been called

[louiscad]

@Martin Devillers async does not spawn a new thread

[Martin Devillers]

@louiscad true, it dispatches to the common pool, so to a different thread…

[louiscad]

@Martin Devillers It's not necessarily a different thread either

[louiscad]

It dispatches to the CoroutineDispatcher it's been assigned to (DefaultDispatcher in the current case where you pass no parameter)

[louiscad]

You can still use async for single thread operations. As long as you have suspension points, it can be useful

[aaverin]

So how do you guys test async methods? I thought wrapping test into runBlocking solves the problem

[Martin Devillers]

The problem is with your mock response here. You have two options:
- Set up the mock to wait until its method is called, do something then
- Set up the mock so that it answers some predefined value once it’s called, without trying to verify immediately that it has been called

[louiscad]

@aaverin I don't write methods that return a Deferred. I use suspend fun instead. I use async for parallel coroutines execution, not in place of suspend fun or launch. If you really need to return a Deferred, be sure to follow the recommendations here: https://github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md#async-style-functions and use await() to await your Deferred inside your coroutine launched inside runBlocking

[aaverin]

What if you know for sure that this function will, eg, go to network, and has to be async?
Sometimes you don’t want to pass threading decision to a consumer of the function

[aaverin]

@louiscad also, in my code I have suspendCoroutine {}. How can I test it then? If I re-write and remove async – this suspendCoroutine still waits forever

[louiscad]

@aaverin async is still not the right solution in this case. Have you read this guide? https://github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md If not, you should

[louiscad]

@aaverin In the rare cases where I need to enforce a certain CoroutineDispatcher inside a suspend fun, I use withContext(theDispatcherIWantHere) { ... }

[louiscad]

If your suspendCoroutine { ... } doesn't resume, it's because resume has not be called, or because the CoroutineDispatcher is blocked somewhere in your code

[aaverin]

well, resume will be called only if I will have chance to mock the response
The way it usually works with RxJava, you call the method, then you catch callback on a mocked instance, and manually call that callback methods to simulate successful network response

[aaverin]

To make it work with coroutines I need to somehow make suspendCoroutine return instantly so I could do the mock magic

[aaverin]

thus my original question – how to test methods with suspendCoroutine?

[louiscad]

I don't use objects mocking right now, so I can't tell you

[gildor]

thus my original question – how to test methods with suspendCoroutine?

I don’t see any problem. You call this method (probably for tests easiest way to wrap this call to runBlocking), you check result of this method