So, I am using coroutines 1.6 and in my data source I have this method ```override fun sumSelectedFe...

# coroutines

[juliocbcotta]

So, I am using coroutines 1.6 and in my data source I have this method

override fun sumSelectedFees(): Single<Float> = rxSingle(workDispatcher) {
    dao.findDeliveryModeShippingOptions(true)
        .fold(0f) { total, shippingOption -> total + shippingOption.feeValue }
}

and I trying to call this in my test

@Test
fun `should sum all inserted fees for delivery`() = runTest {
    val dataSource = dataSource = DeliveryModesDataSourceImpl(dao, UnconfinedTestDispatcher())
    dataSource.sumSelectedFees()
        .test()
        .assertValue(0f)
}

but my test is failing since the test is not waiting the rx call .test() to complete.. I Used UnconfinedTestDispatcher here, but I am not sure what I dispatcher I should be using in this case.

[Sam]

I'm guessing the problem is the workDispatcher you're passing to rxSingle. The test doesn't know anything about that dispatcher and so can't wait for it to finish.

[Sam]

You'll need to find a way to pass the dispatcher from the test into the sumSelectedFees method.

[Sam]

One option would be:

[Sam]

override fun sumSelectedFees(context: CoroutineContext = workDispatcher): Single<Float> = rxSingle(context) {
    ...

[juliocbcotta]

I do pass the Dispatcher in the constructor

val dataSource = DeliveryModesDataSourceImpl(dao, UnconfinedTestDispatcher())

[Sam]

Yeah, I just realised that 🤦 sorry

[Sam]

In that case, I think the problem is just that the UnconfinedTestDispatcher you use isn't the same one being used by runTest

[Sam]

Try to get the existing dispatcher from the TestScope and pass it to the DeliveryModesDataSourceImpl instead of creating a new UnconfinedTestDispatcher

[Sam]

Or create your dispatcher outside the test and pass it into both runTest and the DeliveryModesDataSourceImpl

[juliocbcotta]

I changed my code to use

private val dispatcher = UnconfinedTestDispatcher()

dataSource = DeliveryModesDataSourceImpl(dao, dispatcher)

runTest(dispatcher) {...

Still not working

[Sam]

Maybe after the .test() and before the .assertValue() you need to call runCurrent()

[Sam]

Even the UnconfinedTestDispatcher won't always run all of its coroutines without a call to runCurrent, if they're nested/launched in more complicated ways

[juliocbcotta]

I tried it too, didn't help.

[Sam]

I'm out of ideas then 🤷 sorry! Although I've tested a lot of coroutines, I haven't worked with rxSingle. There must be a trick we're missing.

[juliocbcotta]

Me too, this is so frustrating

[Dmitry Khalanskiy [JB]]

Try UnconfinedTestDispatcher(testScheduler) instead of just UnconfinedTestDispatcher. Otherwise, there's no link between runTest and the dispatcher, unless there's Dispatchers.setMain somewhere.

[juliocbcotta]

I am not calling Dispatchers.setMain , but I am using runTest(dispatcher) , where val dispatcher = UnconfinedTestDispatcher()

[Dmitry Khalanskiy [JB]]

Then UnconfinedTestDispatcher() just creates a new dispatcher, not related to runTest.

[juliocbcotta]

Sorry, I think I didn't understand what you mean. I am just trying to make the test work by connecting the dots... I need the rxSingle to publish in a sync way so .test() will be sync and so my test.
I passed around the Dispatcher to every place I could find, but my tests are still failing.

[Dmitry Khalanskiy [JB]]

@Test
fun `should sum all inserted fees for delivery`() = runTest {
    val dataSource = dataSource = DeliveryModesDataSourceImpl(dao, UnconfinedTestDispatcher(testScheduler)) // <--- modified here
    dataSource.sumSelectedFees()
        .test()
        .assertValue(0f)
}

[juliocbcotta]

My results are the same.

expected: 0.0 (class: Float) but was: [] (latch = 1, values = 0, errors = 0, completions = 0)
java.lang.AssertionError: expected: 0.0 (class: Float) but was: [] (latch = 1, values = 0, errors = 0, completions = 0)

[juliocbcotta]

I think I was able to reproduce the problem with a simpler/more generic version of the code

private val dispatcher = UnconfinedTestDispatcher()

suspend fun bar() = withContext(dispatcher) {
    withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
        1
    }

}

@Test
fun foo() = runTest(dispatcher) {
    rxSingle(dispatcher) { bar() }
        .test()
        .assertValue(1)
        .assertComplete()
}

[Dmitry Khalanskiy [JB]]

This isn't really related to coroutines, this is due to test() in RxJava not awaiting the completion. For example, here is the same issue, without any coroutines:

@Test
    fun foo2() {
        val single = Single.create<Int> { emitter ->
            thread {
                Thread.sleep(10)
                emitter.onSuccess(1)
            }
        }
        single.test().assertValue(1).assertComplete()
    }

It may work if there's only one thread, but <http://Dispatchers.IO|Dispatchers.IO> uses other threads.
This can be fixed with

@Test
fun foo() = runTest(dispatcher) {
    rxSingle(dispatcher) { bar() }
        .test()
        .await() // <-------- waits for completion before checking the results
        .assertValue(1)
        .assertComplete()
}

[juliocbcotta]

Ohh, thanks! I didn't know that!