Hello all. I am running into an issue testing my ...

# android

[Billy Newman]

Hello all. I am running into an issue testing my room paging implementation using mockito. I am following the example laid out here: https://developer.android.com/topic/libraries/architecture/paging/test. Code in thread

[Billy Newman]

In my view model I would like to test the transformation

// watch for filter to change, on charge reset the paging query
   val items = filterParameter.switchMap { filter ->
       Pager(
          config = PagingConfig(pageSize = 20),
          initialKey = null,
          pagingSourceFactory = {
             repository.observeItems(filter)
          }
       ).liveData
    }.asFlow().map { pagingData ->
       pagingData
          .map { item ->
             ListItem(item)
          }
          .insertSeparators { item1: ListItem?, item2: ListItem? ->
             // logic I want to test
          }
    }.cachedIn(viewModelScope)

My test:

@Test
   fun testTransformation() = runTest {

      val repository = mock<MyRepository>()
      `when`(repository.observeItems(Mockito.any()))
         .thenAnswer {
            val flow = flowOf(
               listOf(
                  Item(
                     id = "1",
                     date = Date()
                  )
               )
            )

            val pagingSourceFactory = flow.asPagingSourceFactory(coroutineScope = this)
            pagingSourceFactory()
         }

      val viewModel = MyViewModel(
         repository = repository,
      )

      val items: Flow<PagingData<ListItem>> = viewModel.items
      val snapshot: List<ListItem> = items.asSnapshot() {}

      Assert.assertEquals(1, snapshot.size) // fails as zero items are in the snapshot
   }

This follows the example laid out by android with the exception of using mocks rather than extending the viewmodel. I have verified that the mock is called and the flow is created. However when I grab the snapshot the list of items from the flow is empty.