Features and Changes in Kotest 6.0

This page lists the features and changes in Kotest 6.0.

New Features

Enhanced Concurrency Support

Kotest 6.0 introduces a comprehensive set of concurrency features to improve test execution:

• Spec Concurrency Mode: Controls how specs (test classes) are executed in relation to each other

  • Sequential (default): All specs are executed sequentially
  • Concurrent: All specs are executed concurrently
  • LimitedConcurrency(max: Int): Specs are executed concurrently up to a given maximum number

• Test Concurrency Mode: Controls how root tests within a spec are executed in relation to each other

  • Sequential (default): All tests are executed sequentially
  • Concurrent: All tests are executed concurrently
  • LimitedConcurrency(max: Int): Tests are executed concurrently up to a given maximum number

• Coroutine Dispatcher Factory: Customize the coroutine dispatcher used for executing specs and tests

  • Built-in implementation: ThreadPerSpecCoroutineContextFactory
  • Can be configured at project-wide or spec-level

• Blocking Test Mode: Addresses issues with timeouts when working with blocking code

  • Switches execution to a dedicated thread for the test case
  • Allows the test engine to safely interrupt tests when they time out

Package-Level Configuration

Package-level configuration allows you to define shared configuration that applies to all specs in a specific package and its sub-packages:

• Create a PackageConfig class that extends AbstractPackageConfig in the target package
• Configuration resolution follows a clear hierarchy (test-specific → spec-level → package-level → parent package → global)
• Supports various configuration options (isolation mode, assertion mode, timeouts, etc.)

Shared Test Configuration

The new DefaultTestConfig feature allows you to define shared test configuration that applies to all tests in a spec:

• Set default configuration values like timeout, invocations, tags, etc.
• Individual tests can override any part of the default configuration
• Simplifies configuration management for tests with similar requirements

New Isolation Mode: InstancePerRoot

A new isolation mode InstancePerRoot has been introduced:

• Creates a new instance of the Spec class for every top-level (root) test case
• Each root test is executed in its own associated instance
• Provides better isolation while maintaining a clean structure

TestClock Implementation

A new TestClock implementation has been added for controlling time in tests:

• Mutable Clock that supports millisecond precision
• Allows setting specific instants and manipulating time with plus and minus operations
• Useful for testing time-dependent code in a deterministic way

Enhanced Coroutine Debugging

Improved support for debugging coroutines in tests:

• CoroutineDebugProbeInterceptor for installing the kotlinx debug probe for coroutines
• Helps with debugging by providing stack traces and dumping coroutine information
• Can be enabled on a per-test basis

Decoroutinator Extension

A new extension for improving coroutine stack traces:

• Integrates with Stacktrace Decoroutinator
• Removes internal coroutine implementation details from stack traces
• Makes stack traces cleaner and easier to understand
• Helps quickly identify the source of errors in coroutine-based tests

Power Assert Support

Kotest 6.0 integrates with Kotlin 2.2's Power Assert feature to provide enhanced assertion failure messages:

• Displays values of each part of an expression when an assertion fails
• Makes debugging test failures easier by showing the actual values in the expression
• Works with shouldBe and other configurable assertion functions
• See the Power Assert documentation for details and setup instructions

Breaking Changes

Minimum Versions

Kotest 6.0 requires a minimum of JDK 11 and Kotlin 2.2.

Kotlin Multiplatform Support

The KMP support in Kotest 6.0 has changed from previous versions:

• No longer requires a compiler plugin
• Simplified setup process for multiplatform projects
• See the setup documentation for details

Extensions Publishing

All extensions are now published under the io.kotest group:

• Version cadence tied to main Kotest releases
• Simplifies dependency management
• Affects all extension modules (Allure, Koin, Ktor, MockServer, WireMock, Spring, etc.)

Project Configuration Location

The location of the project config instance is now required to be at a specific path:

• By default will be at io.kotest.provided.ProjectConfig
• Can be overridden by setting the kotest.framework.config.fqn system property
• Will not be picked up by the framework if located elsewhere
• Different from Kotest 5.x behavior

Removed Classpath Scanning

Classpath scanning for extensions has been removed in Kotest 6.0:

• The @AutoScan annotation is no longer supported
• Extensions must now be explicitly registered

To register extensions, use one of these approaches:

• Add extensions to your project config:

  object ProjectConfig : AbstractProjectConfig() {
    override val extensions = listOf(
      MyExtension(),
      AnotherExtension()
    )
  }
• Use the @ApplyExtension annotation on your spec classes:

  @ApplyExtension(MyExtension::class)
  class MySpec : FunSpec() {
    // tests here
  }

Data Driven Testing

If you are using the Kotest 5.0+ withData support, you no longer need to add the kotest-framework-data dependency to your project as this has been merged into the core framework.

Table Driven Testing

If you are using the Kotest 4.x era table driven testing, you will need to add the kotest-assertions-table dependency to your project as this has been moved out of the core framework.

Extension overrides

Inside the project config, extensions are now a val not a function. So if you had before:

override fun listeners() = ...

or

override fun extensions() = ...

Change this to:

override val extensions = ...

Removed listeners

The System.exit and System.env override extensions have been removed due to the deprecation of the SecurityManager in Java.

Deprecated Isolation Modes

The following isolation modes are now deprecated due to undefined behavior in edge cases:

• InstancePerTest
• InstancePerLeaf

It is recommended to use InstancePerRoot instead.

API changes

• Removed io.kotest.assertions.print.Print<A>.print(A, level) in favor of the now-undeprecated print(A).
• Renamed io.kotest.matchers.maps.contain to io.kotest.matchers.maps.mapcontain.
• Moved code from io.kotest:kotest-assertions-api to io.kotest:kotest-assertions-shared, and io.kotest:kotest-assertions-api is artifact is no longer published.
  • io.kotest.matchers.Matcher
  • io.kotest.matchers.MatcherResult
  • io.kotest.matchers.and
  • io.kotest.matchers.or
  • and a few more

Improvements

Coroutine Debug Probes

Enhanced support for coroutine debugging:

• Option to enable debug probes for better visibility into coroutine execution
• Helps identify issues with coroutines in tests
• Provides detailed stack traces and coroutine dumps when errors occur