Top 25 Mobile Testing Interview Questions (with Kotlin Code Samples)

Author: Lamhot Siagian 🔗 LinkedIn

Below are 25 common mobile‐testing questions, each illustrated with a concise Kotlin snippet and a brief explanation.

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1.What is Espresso and how do you write a simple Espresso test in Kotlin?

Answer: Espresso is a UI-testing framework from Google for writing concise, reliable Android UI tests.

@RunWith(AndroidJUnit4::class)
class LoginScreenTest {
  @get:Rule val activity = 
    ActivityScenarioRule(LoginActivity::class.java)

  @Test fun successfulLogin_showsHome() {
    onView(withId(R.id.username)).perform(typeText("user"))
    onView(withId(R.id.password)).perform(typeText("pass"), closeSoftKeyboard())
    onView(withId(R.id.loginButton)).perform(click())
    onView(withText("Welcome")).check(matches(isDisplayed()))
  }
}

We use onView() to find views, perform() to act, and check() to assert.

2.How do you wait for asynchronous operations in Espresso?

Answer: Use an IdlingResource to let Espresso know when your app is idle.

class SimpleIdlingResource : IdlingResource {
  @Volatile private var callback: IdlingResource.ResourceCallback? = null
  private var isIdle = false
  override fun getName() = this::class.java.name
  override fun isIdleNow() = isIdle.also { if (it) callback?.onTransitionToIdle() }
  override fun registerIdleTransitionCallback(cb: IdlingResource.ResourceCallback) {
    callback = cb
  }
  fun setIdleState(idle: Boolean) { isIdle = idle }
}

3.How do you scroll a RecyclerView to a specific item?

onView(withId(R.id.recyclerView))
  .perform(
    RecyclerViewActions.scrollTo<RecyclerView.ViewHolder>(
      hasDescendant(withText("Item 42"))
    )
  )

4.Show a Compose UI test example.

@get:Rule val composeTestRule = createAndroidComposeRule<MainActivity>()

@Test fun counterIncrements() {
  composeTestRule.onNodeWithTag("IncrementBtn").performClick()
  composeTestRule.onNodeWithTag("CounterText")
    .assertTextEquals("Count: 1")
}

5.How do you test a Room database in memory?

@Before fun setup() {
  val context = ApplicationProvider.getApplicationContext<Context>()
  db = Room.inMemoryDatabaseBuilder(context, AppDatabase::class.java).build()
  dao = db.noteDao()
}

@After fun tearDown() = db.close()

6.How do you mock a network call using Retrofit and Mockito?

@Mock lateinit var service: ApiService
@Before fun init() = MockitoAnnotations.openMocks(this)

@Test fun fetchNotes_returnsList() = runBlocking {
`when`(service.getNotes()).thenReturn(listOf(Note(1, "A", "B")))
  val result = service.getNotes()
  assertEquals(1, result.size)
}

7.How do you test a ViewModel in isolation?

@get:Rule val coroutineRule = MainCoroutineRule()

@Test fun loadNotes_updatesState() = coroutineRule.runBlockingTest {
  val fakeRepo = FakeNotesRepository()
  val vm = NotesViewModel(fakeRepo)
  vm.loadNotes()
  assertTrue(vm.state.value.notes.isNotEmpty())
}

8.How do you test an Activity lifecycle?

@Test fun rotateScreen_recreatesActivity() {
  val scenario = ActivityScenario.launch(MainActivity::class.java)
  scenario.onActivity { it.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE }
  scenario.recreate()
  // Assertions after rotation...
}

9.How to take a screenshot during a test?

val device = UiDevice.getInstance(InstrumentationRegistry.getInstrumentation())
device.takeScreenshot(File("/sdcard/test_screenshot.png"))

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10.How do you test deep links?

    @Test fun deepLink_toDetails() {
      val intent = Intent(Intent.ACTION_VIEW).setData("myapp://note/5".toUri())
      ActivityScenario.launch<MainActivity>(intent)
      onView(withText("Note ID: 5")).check(matches(isDisplayed()))
    }

11.How do you test Android WorkManager tasks?

    @Test fun workEnqueues_success() {
      val request = OneTimeWorkRequestBuilder<SyncWorker>().build()
      WorkManager.getInstance(context).enqueue(request).result.get()
      val statuses = WorkManager.getInstance(context).getWorkInfosByTag("sync").get()
      assertEquals(WorkInfo.State.ENQUEUED, statuses.first().state)
    }

12. How to test runtime permissions?

    @Test fun cameraPermission_granted() {
      grantPermission(Manifest.permission.CAMERA)
      onView(withId(R.id.openCamera)).perform(click())
      onView(withText("Camera opened")).check(matches(isDisplayed()))
    }

13.How do you test location updates?

    val fusedLocationClient = mock<FusedLocationProviderClient>()
    whenever(fusedLocationClient.lastLocation).thenReturn(Tasks.forResult(location))

14.How to test notifications?

    val manager = NotificationManagerCompat.from(context)
    val notifications = manager.activeNotifications
    assertTrue(notifications.any { it.id == MY_NOTIFICATION_ID })

15.How do you test dynamic feature modules?

    val splitInstallManager = SplitInstallManagerFactory.create(context)
    assertTrue(splitInstallManager.installedModules.contains("feature_notes"))

16.How to test BLE connections?

    val gatt = mock<BluetoothGatt>()
`when`(gatt.connect()).thenReturn(true)

17.How to test multi-language support?

    @Test fun spanishLocale_showsHola() {
      setLocale("es")
      onView(withId(R.id.greeting)).check(matches(withText("¡Hola!")))
    }

18.How to test dark mode?

    @Test fun darkMode_switchesTheme() {
      composeTestRule.setContent {
        MaterialTheme(colors = darkColors()) { MyApp() }
      }
      // UI assertions in dark theme...
    }

19.How to mock a ViewModel in Compose previews?

    @Preview @Composable
    fun PreviewNotes() {
      NoteAppContent(vm = FakeViewModel())
    }

20.How to test accessibility labels?

    onView(withId(R.id.saveButton))
      .check(matches(withContentDescription("Save note")))

21.How to test rotation with Compose?

    composeTestRule.activityRule.scenario.onActivity {
      it.requestedOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE
    }

22.How to stub network failures?

`when`(service.getNotes()).thenThrow(IOException("Network error"))

23.How do you test database migrations?

    val helper = MigrationTestHelper(
      InstrumentationRegistry.getInstrumentation(),
      AppDatabase::class.java.canonicalName
    )
    helper.createDatabase("test-db", 1).apply { close() }
    helper.runMigrationsAndValidate("test-db", 2, true, MIGRATION_1_2)

24.How to integrate tests into a CI pipeline?

    # in your CI config
    ./gradlew connectedAndroidTest --stacktrace

25.How do you retry flaky tests automatically?

    class RetryRule : TestRule {
      override fun apply(base: Statement, desc: Description) = object : Statement() {
        override fun evaluate() { 
          var caught: Throwable? = null
          repeat(3) {
            try { base.evaluate(); return } catch (e: Throwable) { caught = e }
          }
          throw caught!!
        }
      }
    }

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Each snippet shows a focused strategy for testing a specific area of Android mobile apps with Kotlin.Happy interviewing (and coding)!