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.

• Stack Overflow (don't forget to use the tag "kotest".)
• Kotest channel in the Kotlin Slack (get an invite here)
• Contribute

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.

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

"substring".shouldContain("str")

user.email.shouldBeLowerCase()

myImageFile.shouldHaveExtension(".jpg")

cityMap.shouldContainKey("London")

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.

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
    }
  }
})

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

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

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")

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
  }
})

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

• Test whole collections with Inspectors.
• Write elegant conditions with the matcher DSL: "hello".shouldHaveSubstring("ell").
• Reuse test logic for setup or tear down, with Listeners.
• Test asynchronous code with whenReady and non-deterministic code with eventually or continually
• Let Kotest close resources automatically: val reader = autoClose(StringReader("xyz"))
• Create reusable parameterized tests via test factories
• Handle tricky scenarios such as System Environment with extensions
• Use the Spring extension to automatically inject your spring test classes.
• Test Arrow data types with the Arrow extension.
• Make use of custom plugins for integrations with tools such as Pitest

See our getting started section or full documentation.

Read more about Kotest from third party blogs and articles.