RxCallInstruction.kt

class RxCallInstruction : Instruction() {
    override fun getDescription(): String {
        return "Should wait until login completes."
    }

    override fun checkCondition(): Boolean {
        return RxCounter.isIdle()
    }

}

RxCounter.kt

object RxCounter {

    val counter = AtomicInteger()

    fun increment() {
        counter.getAndIncrement()
    }

    fun decrement() {
        counter.decrementAndGet()
    }

    fun isIdle(): Boolean = counter.get() == 0
}

RxExtensions.kt

fun <T> Observable<T>.testSchedulers(): Observable<T> =
        observeOn(AndroidSchedulers.mainThread())
        .doOnSubscribe { RxCounter.increment() }
        .doAfterTerminate { RxCounter.decrement() }

Test.kt

@LargeTest
@RunWith(AndroidJUnit4::class)
class Test : BaseTest() {
    
    @get:Rule
    val mActivityTestRule = ActivityTestRule(MainActivity::class.java, true, false)
  
    @Before
    fun setUp() {
        val signIn = SignInFragment.newInstance()
        signIn.presenter
                .signIn(validEmail, validPassword, false)
                .testSchedulers()
                .subscribe()
    }
    
    @Test
    fun checkEmptyOrders() {
        ConditionWatcher.waitForCondition(RxCallInstruction())
        mActivityTestRule.launchActivity(Intent())
        testForEmptyOrders()
    }
}