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Version: 5.5 🚧

Release 5.0

This document is a work in progress and will be finalized within a few days of the 5.0 release.

Breaking Changes

Kotlin 1.6 is now the minimum supported version

From version 5 onwards, Kotest requires Kotlin 1.6. The decision to do this is twofold.

Firstly, the main feature in the 5.0 release train is support for multiplatform tests and there are incompatibilities in the compiler between Kotlin 1.5 and 1.6. To support both would add needless complexity to the build.

Secondly, kotlin.time.Duration's have finally gone stable as of 1.6 and Kotest builds on these internally. We wanted to be able to depend on the multiplatform functionality provided by Kotlin durations without any issues arising from changes in these classes from previous versions.

Legacy Javascript compiler support dropped

Javascript support for the legacy compiler is no longer supported. If you are running tests on JS legacy then you will need to continue using Kotest 4.6.x or set your Javascript test build to use only use the IR compiler.

Test support for the legacy Javascript compiler relied on functionality that has been removed in the IR compiler (Namely, that the framework adapter no longer works with third party modules). For the 5.0 release, Kotest provides a compiler plugin which integrates tests directly into the compiled output exactly how the kotlin.test support works.

Global configuration object dropped

In previous versions Kotest supported configuration updates via a global configuration object called configuration (and called project in even earlier versions). From this release onwards, this top level val has been removed.

The reason for the removal is that having global state complicated using multiple instances of the Test Engine in the same JVM and also because there was not precise semanatics around the orders of updates to a top level val.

The former was mainly an issue when testing Kotest itself, since users don't typically create instances of TestEngine directly but instead run tests via gradle or intellij.

This top level val was not included in documentation so users should have been largely unaware it existed anyway. The recommended approach to defining Kotest configuration remains either ProjectConfig or system properties.

Experimental data testing classes moved

The experimental data-test withData functions added in 4.5 under the package name io.kotest.datatest have moved to a new module kotest-framework-datatest.

Note: These are separate from the forAll and forNone data test functions which have been part of Kotest since version 2.0.

Deprecated property test Arb.value removed

The Arb.values() method has been removed from the Arb interface. This method was deprecated in 4.3 in favour of using Arb.sample which was introduced to allow for Arb flat-mapping. This will only affect anyone who has written a custom arb that extends Arb directly and is still using the deprecated method. Any existing uses of the arbitrary builders is unaffected and those builders are always the preferred way to create custom arbitraries.

Startup configuration dump off by default

The Engine no longer logs config to the console during start by default. To enable output, set the system property or env var kotest.framework.dump.config to true.

Deprecated method removals

  • shouldReceiveWithin and shouldReceiveNoElementsWithin channel matchers have been removed.
  • The deprecated RuntimeTagExtension has been undeprecated but moved to a new package.
  • RuntimeTagExpressionExtension has moved to a new package.

Inspector changes.

When using inspectors, the deprecated kotlintest.assertions.output.max system property has been removed. This was replaced with kotest.assertions.output.max in release 4.0 when the project was renamed from KotlinTest to Kotest.


Test Status

The TestStatus enum has been deprecated in favour of the TestResult ADT. Instead of matching onresult.status in AfterTestListener you should now match directly on the result. Eg

when (result) {
is TestResult.Success -> ...
is TestResult.Error -> ...

SpecExtension.intercept(KClass) method deprecation

The intercept(KClass) method in SpecExtension has been deprecated and SpecRefExtension has been added. The deprecated method had ambigious behavior when used with an IsolationMode that created multiple instances of a spec. The new methods have precise guarantees of when they will execute.

  • SpecRefExtensions will execute once per class.
  • SpecExtensions will execute once per instance.

Default test case config

The defaultTestCaseConfig containers in Spec's and project configuration have been deprecated. This is because it was not possible to specify at both the spec level and the project-configuration level and allow settings to fall through.

Instead, you should set per-setting defaults, and these will fall through from test -> spec -> configuration.

For example, instead of this:

class MySpec: FunSpec() {
init {
override fun defaultTestCaseConfig() = TestCaseConfig(tags = setOf(Foo, Bar), timeout = 100.seconds)
test("foo") {
// will time out after 100 seconds and has tags Foo and Bar applied

You should do:

class MySpec: FunSpec() {
init {

tags(Foo, Bar)
timeout = 100.seconds

test("foo") {
// will time out after 100 seconds and has tags Foo and Bar applied

Note that the second variation has always been possible, but the first variation is no longer recommended.

Listener names

The val name inside Listener has been deprecated. This was used so that errors from multiple before/after spec callbacks could appear with customized unique names. The framework now takes ensures that names are unique so this val is no longer needed and is now ignored.

Other deprecations

  • SpecInstantiationListener has been deprecated in favour of InstantiationListener and InstantiationErrorListener, both of which support suspension functions. SpecInstantiationListener is a hold-over from before coroutines existed in Kotlin and so had no support for coroutines.
  • SpecIgnoredListner (note the typo) has been renamed to IgnoredSpecListener.
  • The listeners method to add listeners to a Spec has been deprecated. When adding listeners to specs directly, you should now prefer extensions() rather than listeners().
  • CompareMode /CompareOrder for shouldEqualJson has been deprecated in favor of compareJsonOptions { }