Let's write test code of RxJava!! 1 ~a road to write test using RxJava successfully @sasami! 1 

what steps of writing test code...?! 2 

Steps of writing test code 1. write test function 2. run test 3. test passed!!!!! 3 

Steps of writing test code 1. write test function 2. run test 3. test passed!!!!! ...finish? →There are some cases tests are passed without actually testing...!(especially for RxJava") 4 

Case1 5 

@Test fun checkoutValidations_should_be_VALID_if_hugaProcessor_is_0() { viewModel.checkoutValidations.subscribe { status -> status == CheckoutViewModel.ValidationStatus.VALID } viewModel.hugaProcessor.onNext(0) whenever(service.observeHoge()).thenReturn(Flowable.just(mock())) } 6 

This test will pass!!!!! 7 

! 8 

What are problems? 4 using subscribe() method 4 subscribe() runs asynchronously even in the test code 4 an assertion inside subscribe() is occurred after evaluating test function 9 

How to solve this? 4 use testSubscriber() 4 use Observable.test() method 10 

4 use testSubscriber() val testSubscriber = TestSubscriber() viewModel.checkoutValidations.subscribe(testSubscriber) testSubscriber .assertNoErrors() .assertValue(CheckoutViewModel.ValidationStatus.VALID) 11 

4 use Observable.test() method viewModel.checkoutValidations .test() .assertNoErrors() .assertNotComplete() .assertValue(CheckoutViewModel.ValidationStatus.VALID) 12 

Case2 @Mock private lateinit var hugaProcessor: BehaviorProcessor @Test fun `checkoutValidations should have VALID status if hugaProcessor is 0`() { val testSubscriber = TestSubscriber() viewModel.checkoutValidations.subscribe(testSubscriber) viewModel.hugaProcessor.onNext(0) testSubscriber .assertNoErrors() .assertNotComplete() .assertValue(CheckoutViewModel.ValidationStatus.VALID) } 13 

Case2 @Mock private lateinit var youPay: BehaviorProcessor @Test fun `checkoutValidations should have VALID status if hugaProcessor is 0`() { val testSubscriber = TestSubscriber() viewModel.checkoutValidations.subscribe(testSubscriber) viewModel.hugaProcessor.onNext(0) testSubscriber .assertNoErrors() .assertNotComplete() .assertValue(CheckoutViewModel.ValidationStatus.VALID) } This test is still failed...! 14 

@Mock private lateinit var hugaProcessor: BehaviorProcessor Mocking BehaviorProcessor...? 15 

what are problems? 4 check instance of BehaviorProcessor exists 4 If the instance is mocked, onNext() does not emit any value 16 

How to solve this? private val hugaProcessor: BehaviorProcessor = BehaviorProcessor.create() 17 

Case3 @Test fun callSomeObsevable_should_be_true_if_postTransaction_is_executed() { .... viewModel.callSomeObsevable.subscribe { result -> Assert.assertTrue(result) } viewModel.postTransaction(itemId).test() .assertSubscribed() .assertNoErrors() .assertComplete() } →we want to make sure callSomeObsevable emits true if postTransaction() is called successfully. 18 

@Test fun callSomeObsevable_should_be_true_if_postTransaction_is_executed() { .... viewModel.callSomeObsevable.test() .assertNoErrors() .assertComplete() .assertValue(true) viewModel.postTransaction(itemId).test() .assertSubscribed() .assertNoErrors() .assertComplete() } → We change it like the above like Case1. 19 

@Test fun callSomeObsevable_should_be_true_if_postTransaction_is_executed() { .... viewModel.callSomeObsevable.test() .assertNoErrors() .assertComplete() .assertValue(true) viewModel.postTransaction(itemId).test() .assertSubscribed() .assertNoErrors() .assertComplete() } This test code still fails...! 20 

What are problems? 4 test() method also runs synchronously. So we have to care about the order of the code. 4 So postTransaction() method does not call when assertValue of the first stream is called. 21 

How to fix this? @Test fun callSomeObsevable_should_be_true_if_postTransaction_is_executed() { .... val testSubscriber = viewModel.callSomeObsevable.test() viewModel.postTransaction(itemId).test() .assertSubscribed() .assertNoErrors() .assertComplete() testSubscriber .assertNoErrors() .assertComplete() .assertValue(true) } →before calling postTransaction, we need to subscribe observable function first. 22 

Overview! 4 Use TestSubscriber() 4 don't mock BehaviorProcessor if you want to get from value from it. 4 care about order of the code where subscriber is subscribed 23 

These problems are fixed by this pr...!! 24 

thanks!! 25