kotlin-testing

name	kotlin-testing
description	Kotlin testing patterns with Kotest, MockK, coroutine testing, property-based testing, and Kover coverage. Follows TDD methodology with idiomatic Kotlin practices.
origin	ECC

Kotlin Testing Patterns

Comprehensive Kotlin testing patterns for writing reliable, maintainable tests following TDD methodology with Kotest and MockK.

When to Use

• Writing new Kotlin functions or classes
• Adding test coverage to existing Kotlin code
• Implementing property-based tests
• Following TDD workflow in Kotlin projects

TDD Workflow

RED     -> Write a failing test first
GREEN   -> Write minimal code to pass the test
REFACTOR -> Improve code while keeping tests green

Kotest Spec Styles

StringSpec (Simplest)

class CalculatorTest : StringSpec({
    "add two positive numbers" {
        Calculator.add(2, 3) shouldBe 5
    }
})

BehaviorSpec (BDD Style)

class OrderServiceTest : BehaviorSpec({
    Given("a valid order request") {
        When("the order is placed") {
            Then("it should return a confirmed order") {
                result.status shouldBe OrderStatus.CONFIRMED
            }
        }
    }
})

MockK

val repository = mockk<UserRepository>()
coEvery { repository.findById("1") } returns User(id = "1", name = "Alice")

val service = UserService(repository)
val user = service.getUser("1")
user.name shouldBe "Alice"
coVerify { repository.findById("1") }

Coroutine Testing

class CoroutineServiceTest : FunSpec({
    test("concurrent fetches complete together") {
        runTest {
            val service = DataService(testScope = this)
            val result = service.fetchAllData()
            result.users.shouldNotBeEmpty()
        }
    }
})

Property-Based Testing

class PropertyTest : FunSpec({
    test("string reverse is involutory") {
        forAll<String> { s ->
            s.reversed().reversed() == s
        }
    }
})

Kover Coverage

./gradlew koverHtmlReport
./gradlew koverVerify

Coverage targets: Critical business logic 100%, Public APIs 90%+, General code 80%+.

Best Practices

DO: Write tests FIRST (TDD), use Kotest's spec styles consistently, use MockK's coEvery/coVerify for suspend functions, use runTest for coroutine testing.

DON'T: Mix testing frameworks, mock data classes, use Thread.sleep() in coroutine tests, skip the RED phase in TDD.