How to use MockK to mock an observable - rx-kotlin

Question

I have a data provider that has an Observable<Int> as part of the public API. My class under test maps this into a Observable<String>.
How do I create a mock so that it can send out different values on the data provider's observable?
I can do it using a Fake object, but that is a lot of work that I don't think is necessary with MockK.
Simplified code:
interface DataProvider {
val numberData:Observable<Int>
}
class FakeDataProvider():DataProvider {
private val _numberData = BehaviorSubject.createDefault(0)
override val numberData = _numberData.hide()
// Note: the internals of this class cause the _numberData changes.
// I can use this method to fake the changes for this fake object,
// but the real class doesn't have this method.
fun fakeNewNumber( newNumber:Int ) {
_numberData.onNext( newNumber )
}
}
interface ClassUnderTest {
val stringData:Observable<String>
}
class MyClassUnderTest( dataProvider: DataProvider ):ClassUnderTest {
override val stringData = dataProvider.numberData.map { "string = " + it.toString() }
}
class MockKTests {
#Test fun testUsingFakeDataProvider() {
val fakeDataProvider = FakeDataProvider()
val classUnderTest = MyClassUnderTest( fakeDataProvider )
val stringDataTestObserver = TestObserver<String>()
classUnderTest.stringData.subscribe( stringDataTestObserver )
fakeDataProvider.fakeNewNumber( 1 )
fakeDataProvider.fakeNewNumber( 2 )
fakeDataProvider.fakeNewNumber( 3 )
// Note we are expecting the initial value of 0 to also come through
stringDataTestObserver.assertValuesOnly( "string = 0", "string = 1","string = 2","string = 3" )
}
// How do you write the mock to trigger the dataProvider observable?
#Test fun testUsingMockDataProvider() {
val mockDataProvider = mockk<DataProvider>()
// every { ... what goes here ... } just Runs
val classUnderTest = MyClassUnderTest( mockDataProvider )
val stringDataTestObserver = TestObserver<String>()
classUnderTest.stringData.subscribe( stringDataTestObserver )
// Note we are expecting the initial value of 0 to also come through
stringDataTestObserver.assertValuesOnly( "string = 0", "string = 1","string = 2","string = 3" )
}
}

Answer 1

Try to use following:
every { mockDataProvider.numberData } answers { Observable.range(1, 3) }
And maybe you need to use another way to make a mock object, like this:
val mockDataProvider = spyk(DataProvider())

Answer 2

Do something like this where we create an observable fakelist of the observable
var fakeList :List<Quiz> = (listOf<Quiz>(
Quiz("G1","fromtest","","",1)
))
var observableFakelist = Observable.fromArray(fakeList)
you can then return your observableFakelist.