Test Utilities

StubbedObserver.kt

val singleParamUseCase = ...

// single execution (param is stubbed as "any()")
singleParamUseCase.stubObserver {
    onSuccess("yay")
}

viewModel.triggerSomething()

singleParamUseCase.execute("some-param")

// multi execution

singleParamUseCase.stubObserver("correct") {
    onSuccess("yay")
}

singleParamUseCase.stubObserver("wrong") {
    onError(IllegalStateException())
}

viewModel.triggerSomething()

singleParamUseCase.execute("correct")
singleParamUseCase.execute("wrong")

SubscriptionCountsRule.kt

// Production code

interface Foo {
    fun doFoo(): Completable
}

interface Bar {
    fun doBar(): Completable
}

fun bla(foo: Foo, bar: Bar): Completable =
    foo.doFoo().onErrorComplete().andThen(bar.doBar())

// Test code

val foo = mock<Foo> {
    on { doFoo() } doReturn Completable.error(IllegalStateException())
}
val rule = SubscriptionCountsRule()
val bar = mock<Bar> {
    on { doBar() } doAnswer { inv ->
        rule.ignoredCompletable(inv.identify())
    }
}


bla(foo, bar)
    .test()
    .assertError { it is IllegalStateException }


verify(foo).doFoo()
verify(bar).doBar() // <-- but is it subscribed?!

rule.verifySubscriptionCounts() // <-- now we know!

// Pro Tip: If you include the rule as @Rule into your test, 
// verifySubscriptionCounts() is automatically called after your test ran