v3.4.2 (Sep 21, 2019)
Nov 29, 2015
Jun 26, 2020
KotlinTest (kotlintest)
Ben Bader (benjamin-bader)
David Schreiber-Ranner (davidschreiber)
Pablo Gonzalez Alonso (pablisco)
Juan Ramón González (jrgonzalezg)
Sebastian Schuberth (sschuberth)
Robert Macaulay (taer)
Clément Plantier (clemp6r)
Raúl Raja Martínez (raulraja)
Martin Nonnenmacher (mnonnenmacher)
Thanh Le (lenguyenthanh)
Antonio López Marín (tonilopezmr)
Giacomo Bresciani (brescia123)
Mirko Friedenhagen (mfriedenhagen)
Michael Rozumyanskiy (MichaelRocks)
Robert Elliot (Mahoney)
Jean-Michel Fayard (jmfayard)
Akinori Yamada (stormcat24)
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Source code


Kotest is a flexible and comprehensive testing tool for Kotlin with multiplatform support.

Previously known as Kotlintest - From release 4.0 this project is now known as Kotest

For latest updates see Changelog. Read full documentation or a quick start guide.


Test with Style

Write simple and beautiful tests with the StringSpec style:

class MyTests : StringSpec({
  "length should return size of string" {
    "hello".length shouldBe 5
  "startsWith should test for a prefix" {
    "world" should startWith("wor")

Kotest comes with several testing styles so you can choose one that fits your needs.

Multitude of Matchers

Use over 300 provided matchers to test assertions on many different types:





The withClue and asClue helpers can add extra context to assertions so failures are self explanatory:

withClue("Name should be present") { user.name shouldNotBe null }

data class HttpResponse(val status: Int, body: String)
val response = HttpResponse(200, "the content")
response.asClue {
    it.status shouldBe 200
    it.body shouldBe "the content"

Nesting is allowed in both cases and will show all available clues.

Matchers are extension methods and so your IDE will auto complete. See the full list of matchers or write your own.

Let the Computer Generate Your Test Data

Use property based testing to test your code with automatically generated test data:

class PropertyExample: StringSpec({
  "String size" {
    checkAll<String, String> { a, b ->
      (a + b) shouldHaveLength a.length + b.length

Check all the Tricky Cases With Data Driven Testing

Handle even an enormous amount of input parameter combinations easily with data driven tests:

class StringSpecExample : StringSpec({
  "maximum of two numbers" {
        row(1, 5, 5),
        row(1, 0, 1),
        row(0, 0, 0)
    ) { a, b, max ->
      Math.max(a, b) shouldBe max

Test Exceptions

Testing for exceptions is easy with Kotest:

val exception = shouldThrow<IllegalAccessException> {
  // code in here that you expect to throw an IllegalAccessException
exception.message should startWith("Something went wrong")

Fine Tune Test Execution

You can specify the number of invocations, parallelism, and a timeout for each test or for all tests. And you can group tests by tags or disable them conditionally. All you need is config:

class MySpec : StringSpec({
  "should use config".config(timeout = 2.seconds, invocations = 10, threads = 2, tags = setOf(Database, Linux)) {
    // test here

And More ...

This page gives you just a short overview of Kotest. There are many more features:

See our getting started section or full documentation.

Read more about Kotest from third party blogs and articles.