Kotlin testing patterns with Kotest, MockK, coroutine testing, property-based testing, and Kover coverage. Follows TDD methodology with idiomatic Kotlin practices. Use when writing Kotlin tests with Kotest or MockK, or testing coroutines and checking coverage.

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 Configuring Kover for code coverage How It Works 1. Identify target code — Find the function, class, or module to test 2. Write a Kotest spec — Choose a spec style (StringSpec, FunSpec, BehaviorSpec) matching the test scope 3. Mock dependencies — Use MockK to isolate the unit under test 4. Run tests (RED) — Verify the test fails with the expected error 5. Implement code (GREEN) — Write minimal code to pass the test 6. Refactor — Improve the implementation while keeping tests green 7. Check coverage — Run ./gradlew koverHtmlReport and verify 80%+ coverage Examples The following sections contain detailed, runnable examples for each testing pattern: Quick Reference Kotest specs — StringSpec, FunSpec, BehaviorSpec, DescribeSpec examples in [Kotest Spec Styles]( kotest spec styles) Mocking — MockK setup, coroutine mocking, argument capture in [MockK]( mockk) TDD walkthrough — Full RED/GREEN/REFACTOR cycle with EmailValidator in [TDD Workflow for Kotlin]( tdd workflow for kotlin) Coverage — Kover configuration and commands in [Kover Coverage]( kover coverage) Ktor testing — testApplication setup in [Ktor testApplication Testing]( ktor testapplication testing) TDD Workflow for Kotlin The RED GREEN REFACTOR Cycle Step by Step TDD in Kotlin Kotest Spec Styles StringSpec (Simplest) FunSpec (JUnit like) BehaviorSpec (BDD Style) DescribeSpec (RSpec Style) Kotest Matchers Core Matchers Custom Matchers MockK Basic Mocking Coroutine Mocking Argument Capture Spy and Partial Mocking Coroutine Testing runTest for Suspend Functions Testing Flows TestDispatcher Property Based Testing Kotest Property Testing Custom Generators Data Driven Testing withData in Kotest Test Lifecycle and Fixtures BeforeTest / AfterTest Kotest Extensions Kover Coverage Gradle Configuration Coverage Commands Coverage Targets Code Type Target Critical business logic 100% Public APIs 90%+ General code 80%+ Generated / config code Exclude Ktor testApplication Testing Testing Commands Best Practices DO: Write tests FIRST (TDD) Use Kotest's spec styles consistently across the project Use MockK's coEvery / coVerify for suspend functions Use runTest for coroutine testing Test behavior, not implementation Use property based testing for pure functions Use data class test fixtures for clarity DON'T: Mix testing frameworks (pick Kotest and stick with it) Mock data classes (use real instances) Use Thread.sleep() in coroutine tests (use advanceTimeBy ) Skip the RED phase in TDD Test private functions directly Ignore flaky tests Integration with CI/CD Remember : Tests are documentation. They show how your Kotlin code is meant to be used. Use Kotest's expressive matchers to make tests readable and MockK for clean mocking of dependencies.

kotlin-testing