Why testing matters in Kotlin - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin test function?

Consider this Kotlin function that tests if a number is even. What will be printed when this test runs?

Kotlin

fun isEven(n: Int) = n % 2 == 0

fun testIsEven() {
    val testNumber = 4
    if (isEven(testNumber)) {
        println("Test passed")
    } else {
        println("Test failed")
    }
}

testIsEven()

A Test passed

B Test failed

C Compilation error

D No output

💡 Hint

Think about what the function isEven returns for 4.

The number 4 is even, so isEven(4) returns true. The test prints "Test passed".

🧠 Conceptual

intermediate

Why do we write tests in programming?

Which of the following is the main reason programmers write tests for their code?

A To make the program look more complex

B To make the code run faster

C To check if the code works as expected and catch errors early

D To avoid writing comments

💡 Hint

Think about what testing helps prevent before the program is used.

Tests help find mistakes early and ensure the program behaves correctly.

❓ Predict Output

advanced

What error does this Kotlin test code raise?

Look at this Kotlin test code. What error will it cause when run?

Kotlin

fun divide(a: Int, b: Int): Int = a / b

fun testDivide() {
    val result = divide(10, 0)
    println("Result is $result")
}

testDivide()

A No error, prints 'Result is 0'

B ArithmeticException: / by zero

C Compilation error

D NullPointerException

💡 Hint

What happens if you divide a number by zero in Kotlin?

Dividing by zero causes an ArithmeticException at runtime.

🚀 Application

advanced

How many tests are run in this Kotlin test suite?

Given this Kotlin test suite, how many tests will be executed?

Kotlin

fun testAdd() { println("Add test") }
fun testSubtract() { println("Subtract test") }
fun testMultiply() { println("Multiply test") }

fun runTests() {
    testAdd()
    testSubtract()
}

runTests()

A 2

B 3

C 1

D 0

💡 Hint

Look at which test functions are called inside runTests().

Only testAdd and testSubtract are called, so 2 tests run.

🔧 Debug

expert

What is the value of 'passed' after running this Kotlin test code?

Consider this Kotlin code that tests if numbers are positive. What is the value of the variable passed after running runTests()?

Kotlin

var passed = 0

fun isPositive(n: Int) = n > 0

fun testPositive(n: Int) {
    if (isPositive(n)) {
        passed += 1
    }
}

fun runTests() {
    val numbers = listOf(1, -1, 0, 5)
    for (num in numbers) {
        testPositive(num)
    }
}

runTests()

A 1

B 3

C 4

D 2

💡 Hint

Count how many numbers in the list are greater than zero.

Only 1 and 5 are positive, so passed increments twice.