Room Database Error when espresso test "Cannot access database on the main thread"

Issue

I am using espresso for testing and I am getting an error while executing below method.

viewModel.getData().observe(viewLifecycleOwner, Observer { options ->
            Log.d(TAG, "onViewCreated: $options")
            val data = options.filter { option -> option.type!! == OptionType.DATA}

            updateData.updateUIComponent(data)
        })

get data method return a LiveData object. and this is working fine in the Fragments but not workng in the espresso test class

Cannot access database on the main thread since it may potentially lock the UI for a long period of time.

This is my test class

@LargeTest
@RunWith(AndroidJUnit4::class)
open class BaseIntegrationTest {

    @get:Rule
    val instantTestExecutorRule = InstantTaskExecutorRule()

    lateinit var navController: TestNavHostController

    lateinit var fragmentScenario: FragmentScenario<DetailsFragment>


    @Before
    fun initTest() {

        navController = TestNavHostController(
            ApplicationProvider.getApplicationContext()
        )

    }

    @Test
    fun launchFragment() {

        val bundle = Bundle()

        fragmentScenario =
            launchFragmentInContainer(bundle, themeResId = R.style.Theme_mainTheme)

        fragmentScenario.moveToState(Lifecycle.State.STARTED)

        UiThreadStatement.runOnUiThread {
            navController.setGraph(R.navigation.app_navigation_graph)
        }
        fragmentScenario.onFragment { fragment ->

            //CollectFeedbackFragment()
            Navigation.setViewNavController(fragment.requireView(), navController)
        }

        onView(withId(R.id.progressBar)).isVisible()
    }

}

Solution

I managed to fix this issue By using Dispatchers.IO and Dispatchers.Main

class SampleViewModel : ViewModel() {

    fun getData():DataLiveData {
        viewModelScope.launch {

            withContext(Dispatchers.IO) {

                 // here I am seding the Room db call
                
                withContext(Dispatchers.Main) {
               // I am updating the MutableLiveData object here
                }
            }
        }
        return mutableLiveData
    }
}   

And don't forget to inject dispatchers instead of hardcoding. Click here!

Answered By - Prasa Dev