Why I can not use `+` here? ```abstract class Abs...

# coroutines

[Joan Colmenero]

Why I can not use + here?

abstract class AbstractPresenter<T : PresenterView>(private val uiContext: DefaultDispatcherProvider = DefaultDispatcherProvider()) :
    BasePresenter<T>, CoroutineScope {
    private var job = Job()
    var view: T? = null

    override val coroutineContext: CoroutineContext
        get() = uiContext + job

    override fun onViewDestroyed() {
        this.view = null
        this.job.cancel()
    }

    override fun onViewReady(view: T) {
        this.view = view
    }
}

I was using this before :

abstract class AbstractPresenter<T : PresenterView>(private val uiContext: CoroutineContext = Dispatchers.Main) : BasePresenter<T>, CoroutineScope{..}

And it was working, but the thing is when I'm trying to UnitTest this presenter I can only run one test. If I run my test that contains more than 1 test it will pass only 1, if I run them separately it works, but I want to run them inside the same test and I do not know what I'm missing.

My Presenter looks like this :

class Presenter1(private val usecase: Usecase) :
    AbstractPresenter<Contract.View>(), Contract.Presenter {
    override fun loadData(id: Int?) {
        view?.showProgressBar(isVisible = true)
        launch {
            withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
                usecase.execute(id = id)
            }.fold({
                view?.showProgressBar(isVisible = false)
                view?.showError("Something here")
            }, {
                view?.showProgressBar(isVisible = false)
                view?.displayData(it)
            })
        }
    }
}

The app works, but when trying to unit test this method is giving me error, I've read to use a Rule and I'm using that one :

@ExperimentalCoroutinesApi
class CoroutineTestRule(val testDispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()) : TestWatcher() {

    val testDispatcherProvider = object : DispatcherProvider {
        override fun default(): CoroutineDispatcher = testDispatcher
        override fun io(): CoroutineDispatcher = testDispatcher
        override fun main(): CoroutineDispatcher = testDispatcher
        override fun unconfined(): CoroutineDispatcher = testDispatcher
    }

    override fun starting(description: Description?) {
        super.starting(description)
        Dispatchers.setMain(testDispatcher)
    }

    override fun finished(description: Description?) {
        super.finished(description)
        Dispatchers.resetMain()
        testDispatcher.cleanupTestCoroutines()
    }
}

But what happens? If I migrate to the DispatcherProvider it doesn't let me do the + . What I'm missing?