how can i unit test flows? the following never completes ``` @Test fun listCanBeObserved() ...

# coroutines

[matt tighe]

how can i unit test flows? the following never completes

@Test
    fun listCanBeObserved() = runBlocking {
        dao.insert(thing)

        val data: List<Thing> = dao.observeAll().single()
        val expected = Thing()
        assertEquals(expected, data)
    }

but if I manually collect each emission I can see the assertion is hit successfully in debug mode

fun listCanBeObserved() = runBlocking {
        dao.insert(thing)

        val data: List<Thing> = dao.observeAll().collect {
            val expected = Thing()
            assertEquals(expected, data)
        }
    }

but then the test will never complete

[Dominaezzz]

Use first()

[Dominaezzz]

An observer observes forever, so the flow will never complete. Just get the first emission if that's what you need.

[matt tighe]

that’s not the reason the test won’t complete. copy-paste error but expected is listOf(thing)

[matt tighe]

ah i see, first is a terminal operator. thanks

[matt tighe]

single() is kind of misleading then, i’d expect it to do the same thing

[Dominaezzz]

It kinda does, but it confirms that the flow only emits one item.

[matt tighe]

i see. thanks for your help