Programming language: Kotlin
License: MIT License
Tags: Tests    

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Aspen is a JUnit runner for Kotlin. It's inspired by Ruby's RSpec syntax, the default DSL has a lot more restrictions but you can create your own DSL if it does not fit your needs.

Gradle usage


testCompile "io.damo.aspen:aspen:<version>"

Aspen Spring

testCompile "io.damo.aspen:aspen-spring:<version>"

You will need to use jCenter maven repository

repositories {


If you were to use AssertJ for assertions.

class CompanyControllerTest: Test({

    val mockRepo = mock(CompanyRepository::class.java)
    val controller = CompanyController(mockRepo)


    before {

    describe("#create") {
        test {
            val company = Company(name = "Wayne Enterprises")

            val response = controller.create("Wayne Ent.")

            assertThat(response).isEqualTo(Response(company, true))
            verify(mockRepo).create("Wayne Ent.")

        test("repository creation error") {

            val response = controller.create("Wayne Ent.")

            assertThat(response).isEqualTo(Response(null as Company?, false))

You can focus a test by prefixing changing test to ftest. Then only this or these tests get run. For example running the tests above after replacing the second test with

ftest("repository creation error") {

    val response = controller.create("Wayne Ent.")

    assertThat(response).isEqualTo(Response(null as Company?, false))

Only that second test will get run.

Writing table based tests (a.k.a. Parameterized tests) can be as simple as the following

class ReservationTestExample : Test({

    describe("#amount") {
        class AmountData
        (name: String, val status: Status, val amount: Int) : TestData(name)

        val data = listOf(
            AmountData("when status is OPEN", Status.OPEN, 0),
            AmountData("when status is STARTED", Status.STARTED, 0),
            AmountData("when status is BILLED", Status.BILLED, 100),
            AmountData("when status is PAID", Status.PAID, 100)

        tableTest(data) {


There can only be one before block and it has to be at the top level. describe blocks can only contain test blocks and they cannot be nested further. Unlike RSpec, there are no it blocks. We are trying to encourage having expressive assertions that should describe correctly your expectations.

Why all these restrictions?

The goal of this library is to make your tests a little easier to organize. But we do believe that the JUnit style is sufficient for testing and encourages making your test code clear and easy to read, so we are not adding any unnecessary complexity.

But I want my own DSL!

We tried to make custom Domain Specific Languages easy to write. You can see an example of a second DSL we created allowing nesting by following these links:

Spring Support

Aspen supports Spring!

class SpringApplicationTest : Test({

    val message: String = inject("myMessage")
    val port = injectValue("local.server.port", Int::class)

    val client = OkHttpClient()

    test("GET /hello") {
        val request = Request.Builder()

        val response = client.newCall(request).execute()

        val body = response.body().string()

More examples

You will find actually up-to-date examples that are part of our test suite in the following locations:

Blog posts

What's next?

We have a Pivotal Tracker project, see for yourself