Does anyone know how to correctly test a channel? ...

# coroutines

[dan.the.man]

Does anyone know how to correctly test a channel?

coroutinesTestRule.testDispatcher.runBlockingTest {
            var latestNav: NavEvent? = null
            navChannel.consumeEach {
                latestNav = it }
            vm.handleAction(NearbyListingClicked(nearbyListing))
            assertEquals(latestNav, OpenListing(variant.listing!!.wmid.toString()))
        }

But I'm just getting java.lang.IllegalStateException: This job has not completed yet
The Channel.consumeEach appears to be blocking, which I don't think it should be

[streetsofboston]

the navChannel.consumeEach is not blocking. It is likely suspending (difference there 🙂).
I don’t see all of the code, but if navChannel is never closed (for sending), the consumeEach just keeps being suspended….

[streetsofboston]

You’d need to launch a coroutine within your test-scope and that coroutine should send values to navChannel and close it when needed.

[dan.the.man]

Ah yes that did it thank you! but question, I'm missing something in my understanding

[dan.the.man]

navChannel.consumeEach {
                latestNav = it
                navChannel.close()}  }

So adding that block doesn't fix it, same problem, but wrapping it in a launch block does fix it, which I understand is because the block is now on a different coroutine, and not blocking the test

[dan.the.man]

But I'm not sure why closing it didn't fix that as well

[dan.the.man]

It needs both the channel.close, and to be launched in a separate coroutine. I get that it needs to be closed due to the way the test dispatcher works, but not why it needs to be launched in a separate one

[streetsofboston]

The consumer should not close it. The producer or some other ‘manager’ should.
I think you are looking to just get one value from the channel. Just do latestNav = navChannel.receive()

[dan.the.man]

Yup you're right, it felt bad closing itself, thanks!

[dan.the.man]

coroutinesTestRule.testDispatcher.runBlockingTest {
            val latestEvent = async { navChannel.receive() }
            vm.handleAction(NearbyListingClicked(nearbyListing))
            assertEquals(latestEvent.await(), OpenListing(variant.listing!!.wmid.toString()))
        }

Ended up going with this and it's all working as expected, thanks!