Hey folks I m using mockito to mock a viewmodel and then ret

Question

Hey folks I m using mockito to mock a viewmodel and then return certain values my view model contains this where imageItems is ```var imageItems List lt ImageItem gt by mutableStateOf listOf private set``` and then my mock looks like this ``` Mock lateinit var viewModel ImageListViewModel `when` viewModel imageItems thenReturn listOf ``` but doing this gives me an error ```java lang NullPointerException Attempt to invoke interface method java lang Object androidx compose runtime State getValue on a null object reference``` would anyone know what I m doing wrong

Gabriel · Answer

If I try skipping the mocking of the values I now instead get ```java lang IllegalArgumentException Cannot skip the enclosing group while in an empty region at androidx compose runtime SlotReader skipToGroupEnd SlotTable kt 222 ```

Zach Klippenstein (he/him) [MOD] · Answer

I would use StateFlow in your view model instead of MutableState it will probably much more straightforward to mock since it doesn t depend on all the snapshot magic in compose

Zach Klippenstein (he/him) [MOD] · Answer

Then in compose you can call collectAsState to convert it to a State

Gabriel · Answer

OK I ll have a look at that thanks < Zach Klippenstein he him MOD >

Gabriel · Answer

< Zach Klippenstein he him MOD > still the same similar problem ```java lang NullPointerException Attempt to invoke interface method java lang Object kotlinx coroutines flow StateFlow getValue on a null object reference at co g403 android minderachallengev3 imageList ImageListScreenKtTest imageListScreen ImageListScreenKtTest kt 29 at java lang reflect Method invoke Native Method at org junit runners model FrameworkMethod$1 runReflectiveCall FrameworkMethod java 50 at org junit internal runners model ReflectiveCallable run ReflectiveCallable java 12 at org junit runners model FrameworkMethod invokeExplosively FrameworkMethod java 47 at org junit internal runners statements InvokeMethod evaluate InvokeMethod java 17 ```

Gabriel · Answer

``` `when` viewModel isLoading value thenReturn false ```

Gabriel · Answer

``` private val isLoading = MutableStateFlow false val isLoading StateFlow lt Boolean gt get = isLoading```

Zach Klippenstein (he/him) [MOD] · Answer

Don t provide mocks for the members of the StateFlow just provide a MutableStateFlow to your ViewModel mock

Gabriel · Answer

< Zach Klippenstein he him MOD > sorry could you explain that a bit more

Zach Klippenstein (he/him) [MOD] · Answer

Don t do `when viewModel isLoading value the return false ` instead do ```private val isLoading = MutableStateFlow false when viewModel isLoading thenReturn isLoading ```

Zach Klippenstein (he/him) [MOD] · Answer

And just configure your fake loading value using the regular MutableStateFlow API

Gabriel · Answer

OK thanks I ll give that a try

Gabriel · Answer

```org mockito exceptions misusing MissingMethodInvocationException when requires an argument which has to be a method call on a mock ```