Testando Flows =)

TestandoFlows.kt

class TestandoSharedFlow(val useCase: TestandoSharedFlowUseCase) : ViewModel() {
    private val states = MutableSharedFlow<Int>(
        onBufferOverflow = BufferOverflow.DROP_LATEST,
        extraBufferCapacity = 1
    )

    fun observeStates() = states.asSharedFlow()

    fun addToStates(number: Int) {
        viewModelScope.launch {
            val resultado = useCase.somaUmAoNumeroRecebido(number)
            states.emit(resultado)
        }
    }

}

class TestandoSharedFlowUseCase {
    suspend fun somaUmAoNumeroRecebido(number: Int): Int {
        val teste = number
        withContext(Dispatchers.IO) {
            teste + 1
        }
        return teste
    }
}

@RunWith(JUnit4::class)
class TestandoSharedFlowTest {

    val useCase: TestandoSharedFlowUseCase = mockk()
    val minhaClasse = TestandoSharedFlow(useCase)

    @Before
    fun init() {
        Dispatchers.setMain(UnconfinedTestDispatcher())
        MockKAnnotations.init(this)
    }

    @After
    fun tearDown() {
        Dispatchers.resetMain() // reset the main dispatcher to the original Main dispatcher
    }

    @Test
    fun `testando a emissao dos valores`() = runTest {
        // setup
        val list = mutableListOf<Int>()

        coEvery { useCase.somaUmAoNumeroRecebido(1) } returns 2
        coEvery { useCase.somaUmAoNumeroRecebido(2) } returns 3
        coEvery { useCase.somaUmAoNumeroRecebido(3) } returns 4

        // convert os states em uma lista de emissões
        val job = launch(UnconfinedTestDispatcher(testScheduler)) {
            minhaClasse.observeStates().toList(list)
        }

        // roda os cenários
        minhaClasse.addToStates(1)
        minhaClasse.addToStates(2)
        minhaClasse.addToStates(3)
        minhaClasse.addToStates(3)
        runCurrent() // resume as threads de emissao

        assertTrue(list[0] == 2)
        assertTrue(list[1] == 3)
        assertTrue(list[2] == 4)
        assertTrue(list[3] == 4)
        // faz os asserts e para de observar o job lançado anteriormente
        job.cancel()
    }
}