Kotlin test assertions - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin test assertion code?

Consider the following Kotlin test code using JUnit assertions. What will be the output when this test runs?

Kotlin

import org.junit.jupiter.api.Assertions.*
import org.junit.jupiter.api.Test

class SampleTest {
    @Test
    fun testSum() {
        val result = 2 + 3
        assertEquals(5, result)
        assertTrue(result > 4)
        assertFalse(result < 0)
    }
}

A Test passes with no errors

B Test fails with AssertionError on assertEquals

C Test fails with AssertionError on assertTrue

D Test fails with AssertionError on assertFalse

💡 Hint

Check the values compared in the assertions carefully.

The sum 2 + 3 equals 5, so assertEquals(5, result) passes. result > 4 is true, so assertTrue passes. result < 0 is false, so assertFalse passes. All assertions succeed, so the test passes.

❓ Predict Output

intermediate

What error does this Kotlin test assertion code raise?

What error will be raised when running this Kotlin test code?

Kotlin

import org.junit.jupiter.api.Assertions.*
import org.junit.jupiter.api.Test

class SampleTest {
    @Test
    fun testString() {
        val actual = "Kotlin"
        assertEquals("kotlin", actual)
    }
}

A No error, test passes

B NullPointerException

C AssertionError due to case mismatch

D Compilation error

💡 Hint

assertEquals is case sensitive for strings.

The expected string "kotlin" is lowercase, but actual is "Kotlin" with uppercase K. assertEquals fails and throws AssertionError.

🔧 Debug

advanced

Why does this Kotlin test assertion fail unexpectedly?

This Kotlin test code fails with an AssertionError. Identify the reason.

Kotlin

import org.junit.jupiter.api.Assertions.*
import org.junit.jupiter.api.Test

class SampleTest {
    @Test
    fun testList() {
        val list1 = listOf(1, 2, 3)
        val list2 = listOf(3, 2, 1)
        assertEquals(list1, list2)
    }
}

A Lists have same elements but different order

B Lists have different sizes

C assertEquals cannot compare lists

D Compilation error due to missing import

💡 Hint

assertEquals compares lists element by element in order.

Although both lists contain the same numbers, their order differs. assertEquals compares elements in order, so the test fails.

📝 Syntax

advanced

Which option correctly asserts that a nullable variable is null in Kotlin test?

Given a nullable variable val name: String? = null, which assertion correctly checks it is null?

A assertNull(name)

B assertEquals(null, name)

C assertTrue(name == null)

D All of the above

💡 Hint

Check which assertions are valid and equivalent for null checks.

assertNull(name) explicitly checks for null. assertEquals(null, name) compares to null. assertTrue(name == null) checks condition. All are valid ways to assert null.

🚀 Application

expert

What is the output of this Kotlin test assertion with exception checking?

What will happen when running this Kotlin test code that checks for an exception?

Kotlin

import org.junit.jupiter.api.Assertions.*
import org.junit.jupiter.api.Test

class SampleTest {
    @Test
    fun testException() {
        val exception = assertThrows<IllegalArgumentException> {
            throw IllegalArgumentException("Invalid argument")
        }
        assertEquals("Invalid argument", exception.message)
    }
}

A Test fails due to message mismatch

B Test passes with no errors

C Test fails due to wrong exception type

D Test fails because no exception is thrown

💡 Hint

assertThrows expects the specified exception type to be thrown inside the lambda.

The code throws IllegalArgumentException with message "Invalid argument". assertThrows catches it and returns the exception. The message matches, so all assertions pass.