Instrumented tests in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this instrumented test?

Consider this Android instrumented test code snippet. What will the test verify and what is the expected result?

Android Kotlin

import androidx.test.ext.junit.runners.AndroidJUnit4
import androidx.test.rule.ActivityTestRule
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith
import androidx.test.espresso.Espresso.onView
import androidx.test.espresso.assertion.ViewAssertions.matches
import androidx.test.espresso.matcher.ViewMatchers.withText
import androidx.test.espresso.matcher.ViewMatchers.withId

@RunWith(AndroidJUnit4::class)
class MainActivityTest {
  @get:Rule
  val activityRule = ActivityTestRule(MainActivity::class.java)

  @Test
  fun checkHelloTextDisplayed() {
    onView(withId(R.id.textView)).check(matches(withText("Hello World")))
  }
}

A The test will fail because ActivityTestRule is deprecated and cannot be used.

B The test checks if the TextView with id textView is clickable and passes if true.

C The test verifies if the MainActivity launches without crashing but does not check UI text.

D The test checks if the TextView with id textView displays "Hello World" and passes if true.

💡 Hint

Look at the onView and check methods to see what UI element and property are tested.

The test uses Espresso to find a view by its id and checks if its text matches "Hello World". If the text matches, the test passes.

❓ lifecycle

intermediate

What happens when an instrumented test uses ActivityScenario.launch()?

In Android instrumented tests, what is the effect of calling ActivityScenario.launch(MainActivity::class.java)?

A It launches MainActivity but does not allow interaction with UI elements.

B It only creates an instance of MainActivity but does not start it.

C It launches the MainActivity and manages its lifecycle automatically for testing.

D It launches MainActivity but immediately finishes it, so tests cannot run.

💡 Hint

Think about how ActivityScenario helps with lifecycle in tests.

ActivityScenario.launch() starts the activity and handles lifecycle states, allowing tests to interact with the UI safely.

🔧 Debug

advanced

What error will this instrumented test produce?

Given this instrumented test code, what error will occur when running it?

Android Kotlin

import androidx.test.ext.junit.runners.AndroidJUnit4
import androidx.test.rule.ActivityTestRule
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith
import androidx.test.espresso.Espresso.onView
import androidx.test.espresso.matcher.ViewMatchers.withId
import androidx.test.espresso.action.ViewActions.click

@RunWith(AndroidJUnit4::class)
class ButtonClickTest {
  @get:Rule
  val activityRule = ActivityTestRule(MainActivity::class.java)

  @Test
  fun clickButton() {
    onView(withId(R.id.nonExistentButton)).perform(click())
  }
}

A No error, test passes because the button exists.

B RuntimeException: NoMatchingViewException because the button with id nonExistentButton is not found.

C Compilation error because R.id.nonExistentButton is undefined.

D Test fails with NullPointerException due to missing activityRule.

💡 Hint

Check what happens if Espresso tries to find a view that does not exist.

Espresso throws NoMatchingViewException at runtime if the view with the given id is not found in the current activity.

❓ navigation

advanced

Which option correctly tests navigation between two activities?

You want to write an instrumented test that verifies clicking a button in MainActivity opens DetailActivity. Which code snippet correctly tests this navigation?

A

onView(withId(R.id.openDetailButton)).perform(click())
onView(withId(R.id.detailRootLayout)).check(matches(isDisplayed()))

B

onView(withId(R.id.openDetailButton)).perform(click())
onView(withId(R.id.mainRootLayout)).check(matches(isDisplayed()))

C

onView(withId(R.id.openDetailButton)).perform(click())
assertEquals(currentActivity, MainActivity::class.java)

D

onView(withId(R.id.openDetailButton)).perform(click())
assertEquals(currentActivity, DetailActivity::class.java)
onView(withId(R.id.detailRootLayout)).check(matches(isDisplayed()))

💡 Hint

Think about how to verify the new activity's UI is shown after clicking the button.

After clicking the button, checking that a view unique to DetailActivity is displayed confirms navigation succeeded.

🧠 Conceptual

expert

What is the main difference between local unit tests and instrumented tests in Android?

Choose the best explanation of the key difference between local unit tests and instrumented tests.

A Local unit tests run on the JVM without Android framework, instrumented tests run on a device or emulator with full Android environment.

B Local unit tests can test UI components, instrumented tests cannot test UI.

C Local unit tests require a device or emulator, instrumented tests run on the JVM only.

D Local unit tests are slower than instrumented tests because they run on devices.

💡 Hint

Consider where each test type runs and what environment they have access to.

Local unit tests run on your computer's JVM and cannot access Android framework classes, while instrumented tests run on real or virtual devices with Android OS.