Why testing ensures app reliability in Android Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple unit test function in Kotlin.

Android Kotlin

fun testAddition() {
    val result = 2 + 2
    assertEquals([1], result)
}

Drag options to blanks, or click blank then click option'

A5

B6

C4

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong expected value in assertEquals.

Forgetting to use assertEquals for comparison.

The test checks if 2 + 2 equals 4, which is the correct result.

2fill in blank

medium

Complete the code to launch an activity in an Android instrumented test.

Android Kotlin

val scenario = ActivityScenario.launch([1]::class.java)

Drag options to blanks, or click blank then click option'

AApplication

BMainActivity

CContext

DView

Attempts:

3 left

💡 Hint

Common Mistakes

Using Application or Context instead of an Activity class.

Using a view class instead of an activity.

ActivityScenario.launch requires the activity class to launch, here MainActivity.

3fill in blank

hard

Fix the error in the test assertion to check if a list contains a value.

Android Kotlin

assertTrue(myList.[1](5))

Drag options to blanks, or click blank then click option'

Acontains

Bhas

Cincludes

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent functions like has or includes.

Confusing Kotlin with JavaScript syntax.

The correct Kotlin function to check if a list contains an element is contains().

4fill in blank

hard

Fill both blanks to create a test that checks if a function throws an exception.

Android Kotlin

assertThrows<[1]> {
    myFunction([2])
}

Drag options to blanks, or click blank then click option'

AIllegalArgumentException

B5

C0

DNullPointerException

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception type in assertThrows.

Passing a value that does not cause an exception.

The test expects an IllegalArgumentException when myFunction is called with 0.

5fill in blank

hard

Fill all three blanks to create a test that verifies a LiveData value changes correctly.

Android Kotlin

val liveData = MutableLiveData<Int>()
liveData.value = [1]
liveData.observeForever { value ->
    assertEquals([2], value)
}
liveData.value = [3]

Drag options to blanks, or click blank then click option'

A0

B1

Attempts:

3 left

💡 Hint

Common Mistakes

Not updating LiveData value before observing.

Expecting the wrong value in assertEquals.

The LiveData starts at 0, then changes to 1, and the observer checks for 1.

Practice

1. Why is testing important for mobile apps?

easy

A. It changes the app design automatically

B. It finds problems before users see them

C. It makes the app run faster

D. It removes all bugs without coding

Solution

1. Step 1: Understand the purpose of testing

   Testing helps find errors or bugs early in development before users encounter them.

2. Step 2: Compare options to testing benefits

   Only It finds problems before users see them correctly states that testing finds problems before users see them, which improves app reliability.

3. Final Answer:

   It finds problems before users see them -> Option B

4. Quick Check:

   Testing = Finds problems early [OK]

Hint: Testing catches bugs early to protect users [OK]

Common Mistakes:

• Thinking testing speeds up the app
• Believing testing changes app design
• Assuming testing removes bugs automatically

2. Which Kotlin syntax correctly defines a simple test function?

easy

A. fun testExample() assert(true)

B. test fun example() { assertTrue() }

C. fun exampleTest { assertTrue(true) }

D. fun testExample() { assert(true) }

Solution

1. Step 1: Review Kotlin function syntax

   A function starts with 'fun', followed by name and parentheses, then braces for body.

2. Step 2: Check each option for correct syntax

   fun testExample() { assert(true) } uses correct syntax: 'fun testExample() { assert(true) }'. Others have syntax errors like missing parentheses or wrong order.

3. Final Answer:

   fun testExample() { assert(true) } -> Option D

4. Quick Check:

   Correct Kotlin function syntax = fun testExample() { assert(true) } [OK]

Hint: Look for 'fun name() { }' pattern in Kotlin [OK]

Common Mistakes:

• Omitting parentheses after function name
• Placing 'fun' keyword incorrectly
• Missing braces around function body

3. What will this Kotlin test code print if the app crashes on null input?

fun testNullInput() {
  val input: String? = null
  val result = input!!.length
  println("Test passed")
}

medium

A. NullPointerException error

B. No output

C. 0

D. Test passed

Solution

1. Step 1: Understand the '!!' operator in Kotlin

   The '!!' forces a nullable variable to non-null, throwing NullPointerException if null.

2. Step 2: Analyze the code behavior with null input

   Since input is null, 'input!!' throws NullPointerException before printing anything.

3. Final Answer:

   NullPointerException error -> Option A

4. Quick Check:

   '!!' on null = NullPointerException [OK]

Hint: Remember '!!' crashes if value is null [OK]

Common Mistakes:

• Assuming code prints 'Test passed' anyway
• Thinking null length is zero
• Ignoring exception from '!!' operator

4. This test function is supposed to check if a list is empty, but it fails. What is the error?

fun testEmptyList() {
  val list = listOf<Int>()
  assert(list.isNotEmpty())
}

medium

A. Missing parentheses after listOf

B. Using assert instead of assertTrue

C. Wrong assertion condition for empty list

D. List should be mutable

Solution

1. Step 1: Understand the test goal

   The test wants to check if the list is empty, so it should assert that list is empty.

2. Step 2: Check the assertion condition

   Current code asserts list.isNotEmpty(), which is false for an empty list, causing test failure.

3. Final Answer:

   Wrong assertion condition for empty list -> Option C

4. Quick Check:

   Test empty list = assert(list.isEmpty()) [OK]

Hint: Match assertion to test goal carefully [OK]

Common Mistakes:

• Confusing isEmpty() with isNotEmpty()
• Using wrong assert function
• Thinking listOf needs parentheses fix

5. You want to ensure your app still works after adding a new feature. Which testing approach best helps keep reliability?

hard

A. Write unit tests for existing and new code

B. Only test the new feature manually

C. Skip tests and fix bugs after release

D. Test only on one device model

Solution

1. Step 1: Understand how to keep app reliable after changes

   Testing existing and new code with unit tests helps catch bugs early and ensures features work together.

2. Step 2: Evaluate options for best practice

   Write unit tests for existing and new code covers both existing and new code with automated tests, which is best for reliability.

3. Final Answer:

   Write unit tests for existing and new code -> Option A

4. Quick Check:

   Unit tests for all code = reliability [OK]

Hint: Test all code, not just new parts [OK]

Common Mistakes:

• Testing only new features manually
• Ignoring tests until after release
• Testing on limited devices only