Property-based testing library for Kotlin.

Main features:

  • Test-engine agnostic
  • Multiplatform
  • No reflection
  • Configurable built-in generators
  • Easy way to create and combine generators
  • Seeded generation for reproducible results

Planned features:

  • Shrinking

Have a look at the setup and usage


The project is incubating and its API is subject to changes.

Please give it a try and write a feedback in the issues.

For mode details about the future of kwik, here’s a roadmap.

How it looks like

class PlusOperatorTest {

    fun isCommutative() = forAll { x: Int, y: Int ->
        x + y == y + x

    fun isAssociative() = forAll(iterations = 1000) { x: Int, y: Int, z: Int ->
        (x + y) + z == x + (y + z)

    fun zeroIsNeutral() = forAll(seed = -4567) { x: Int ->
        x + 0 == x

For more information, read how to write tests and have a look at the available generators


Property based testing is great and very powerful. But despite the fact that many good libraries already exist, none of them fully fit my needs.

The known alternatives either:

  • Are bound to a specific test-engine
  • Can only be used when compiling kotlin to Java (and cannot be used in multi-platform projects)
  • Relies on reflection, making the tests slower and make some errors detectable only at runtime
  • Do not allow enough freedom and safety to customize existing generators
  • Force the user to add unwanted dependencies in the classpath


  • Kotlin version: 1.4.0 or newer
  • JDK version: 8, 11 or 15


Example of setup using gradle.

repositories {

dependencies {

For more information, read the setup


See how to contribute