Why and What to Test

Why and What to Test

In this lesson — part of Testing Fundamentals — you'll learn why and what to test in Kotlin and why it matters in real work.

Why it matters

Tests prove your code works and keep it working as you change it.

Key ideas

• What to test
• Arrange-Act-Assert
• Running a test suite
• Good vs. brittle tests

In practice

Here's how it looks in idiomatic Kotlin:

import kotlin.test.Test
import kotlin.test.assertEquals

class MathTest {
    @Test
    fun adds() {
        assertEquals(7, 3 + 4)
    }
}

Kotlin note: The multiplatform kotlin.test library provides @Test and assertions that delegate to JUnit on the JVM, so tests stay framework-agnostic.

Try it yourself

Exercise: In Kotlin, write three tests for a function that reverses a string.

Recap

You now understand why and what to test and can apply it in Kotlin. Mark this lesson complete and continue to the next one.