How to test Kotlin Coroutine actors

Question

I've implemented an actor like in the official kotlinx.coroutines docs. Now I have to test them inside of my instrumented tests, but I'm always getting

IllegalStateException: This job has not completed yet

Here's my test code:

@RunWith(AndroidJUnit4::class)
@ExperimentalCoroutinesApi
class ExampleInstrumentedTest {

    @Test
    fun testIncrease() = runBlockingTest {
        val counter = Counter()
        for (i in 0..10) {
            counter.increase()
        }
    }

    @Test
    fun testException() = runBlockingTest {
        val counter = Counter()
        try {
            for (i in 0..11) {
                counter.increase()
            }
            Assert.fail()
        } catch (e: Exception) {
            // All good if the exception was thrown
        }
    }
}

And here's the actor:

sealed class CounterMsg
object IncCounter : CounterMsg()
class GetCounter(val response: CompletableDeferred<Int>) : CounterMsg()

class CounterActor {
    private val actor = GlobalScope.actor<CounterMsg> {
        var counter = 0
        for (msg in channel) {
            when (msg) {
                is IncCounter -> if (counter < 10) counter++ else throw RuntimeException()
                is GetCounter -> msg.response.complete(counter)
            }
        }
    }

    suspend fun send(message: CounterMsg) = actor.send(message)
}

class Counter {
    private val actor = CounterActor()
    suspend fun increase() = actor.send(IncCounter)
}

My dependencies:

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.40"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-jdk8:1.3.0-M1"
androidTestImplementation "androidx.test.ext:junit:1.1.1"
androidTestImplementation "androidx.test:runner:1.2.0"
androidTestImplementation "org.jetbrains.kotlin:kotlin-test:1.3.40"
androidTestImplementation "org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.0-M1"

I've already tried GlobalScope.actor<CounterMsg>(Dispatchers.Unconfined) which at least will turn the first test to green, but the exception test is still failing.

Answer 1

I solved by adding following rule:

@get: Rule
var instantExecutorRule = InstantTaskExecutorRule()

Answer 2

Apparently, it's working with some small changes:

• Use cancel() instead of throwing an exception in the actor
• Use runBlocking instead of runBlockingTest