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Version: 5.7


5.7.2 September 2023


  • Revert to build against JDK 1.8
  • Removed autoscan warning

5.7.1 September 2023


  • Fix timeout detection when withTimeout wraps a blocking job (#3675)
  • Use object equals by default (#3671)

5.7.0 September 2023


  • Refactor concurrency #3623
  • Add support of Equality to all contain* matchers (#3662)
  • Added shouldBeEqualUsingFields (#3652)
  • Add nullable type support to test functions (#3665)
  • Compose Matcher.any (#3664)
  • Make Matcher.all multi-platform (#3663)
  • Allow nested jar scanning by configuration (#3644)
  • Bind BlockHoundMode setting to coroutines, lifting restrictions (#3622)
  • Add sequence version of monotonic/strictly inc/dec (#3645)
  • Added reworked non-deterministic functions (#3597)
  • Added warning for autoscan #3640
  • Add expect block to skip tests (#3596)
  • Add includeNonFiniteEdgeCases flag for double and float arbitrary (#3638)
  • Arb.offsetDateTime based on Instant (#3632)
  • Reimplement KProperty0<T>.shouldHaveValue as matcher (#3637)
  • Add more java.time supports for reflective bind (#3636)
  • Add KProperty0 assertions (#3621)
  • Arb.list implementation supporting Arb<IntRange> and Arb.intRange (#3618)
  • Added config options for retry (#3600)
  • implemented beforeInvocation and afterInvocation hooks (#3589)
  • add Arb<Date> support (#3554)
  • Adding support for partial permutations (#3523)
  • add exhaustive enumsExcept (#3552)


  • Fix order of afterXX callbacks (#3639)
  • Updated NaN handling in assertions (#3661)
  • Only invoke beforeSpec if a test is invoked (#3649)
  • Filter out success in matcher.all (#3646)
  • Add allowOutOfOrderCallbacks (#3642)
  • Updated docs for RgxGen #3607
  • Added see-difference formatting for shouldHaveSingleElement (#3599)
  • Use the default spec for the first test in InstancePerTest (#3601)
  • Throw error if @Order is used without specifying spec execution order (#3641)
  • feat: map matchers (all or exactly) allow dynamic matchers (#3569)
  • extra properties are not tolerated with different array ordering (#3629)
  • Rewrite System Extensions docs for more clarity (#3630)
  • matchJsonResource should check file existence (#3634)
  • Fix nullable reflective binds not working some supported types (#3635)
  • Fix extension processing order, prioritize test case config (#3613) (#3614)
  • Fix duration shrinker so it shrinks (#3611)
  • Fix name of withDefaultTimeZone in docs (#3615)
  • Undeprecating shouldEqualSpecifiedJson. #3543
  • Correcting reporting of errors from BeforeSpec when using InstancePerTest spec (#3585)
  • Rename Data Class Matchers to Composed Matchers (#3406)
  • Fix outdated option in the jacoco documentation #3539
  • Fixing TestAbortedException not being marked as Ignored (#3587)
  • Removing workaround for using @Language for MPP (#3591)
  • Feature/improve arrow documentation (#3570)
  • Add fix to handle scenario where no tags are present in the runtime tags, but some specs are annotated with @RequiresTag() (#3532)
  • Making NamedTag a data class, so it gets equals() (#3579)
  • Adding indices of elements in inspectors failure messages (#3578)
  • Fix CollectingTestEngineListener retaining all the Specs (#3573)
  • fmap matchers allow null value (#3568)
  • fix IrLinkageError with K/Js on Kotlin 1.9 (#3557)
  • fix annotation typo and add link to Spring docs (#3551)
  • Bugfix/add char to platformstable types (#3536)
  • updating lib name from 'Test containers' to 'Testcontainers' (#3545)
  • Fixing test that was broken after previous commit
  • Fix documented annotation as @RequireTags which should be @RequiresTag (#3530)
  • fix reflective bind failing on sealed class with object member (#3529)
  • Adding changelog for v5.6.2 (#3519)

Thank you to all contributors since the 5.6.0 release

  • AJ Alt
  • Alexey Yakovlev
  • Alphonse Bendt
  • aSemy
  • Ayushi Gupta
  • Charles Korn
  • Claudenir Freitas
  • Cory Thomas
  • David Weber
  • Dmitry Spikhalskiy
  • Emil Kantis
  • Erik Huizinga
  • hughlunnon
  • Israel José Boiko
  • Just.Viktor
  • Karl-Philipp Richter
  • ktrueda
  • Leonardo Colman Lopes
  • Łukasz Pięta
  • Łukasz Wasylkowski
  • Matej Drobnič
  • Mikael Elm
  • Mitchell Yuwono
  • OliverO2
  • Paolo Simonazzi
  • Rafał Prominski
  • sksamuel
  • Thom
  • Viktors Garkavijs
  • Vladislav Krasov
  • Zak Henry

5.6.2 May 2023


Property testing



⚠️ Reverted behavior of Arb.string()

With Kotest 5.6.0, Codepoint.ascii() was changed to include a wider range of ascii chararacters, and Codepoint.printableAscii() was introduced with the historic range used by Codepoint.ascii().

Arb.string() has been using Codepoint.ascii() as it's default for generating chars for the string. This caused issues for some users, and we decided to revert Arb.string() to the historic behavior by changing the default to the new Codepoint.printableAscii().

Hopefully this doesn't cause any issues for you. If it does, you can revert to the 5.6.0 ~ 5.6.1 behavior by using Codepoint.ascii() explicitly.

If you added explicit usage of Codepoint.printableAscii() to circumvent the issue, you can safely remove the explicit parameter starting with Kotest 5.6.2.

New Contributors

Full Changelog:

5.6.1 April 2023

This release is mainly to add some missing klib dependencies for ios


  • add language annotation to json matchers (#3487)

5.6.0 April 2023

Note this release bumps the minimum required version of Kotlin to 1.8.0. If you are using < 1.8.0 you can continue to use Kotest 5.5.x

Breaking changes:

  • Moved ConstantNow-related functions to a new module named io.kotest:kotest-extensions-now (remember to add -jvm suffix for Maven)
    • Add this module as a dependency to keep using withConstantNow
  • Remove Iterable checking logic from IterableEq (#3420)


  • BlockHound extension: Fix handling of nested tests (#3454) (#3456)
  • fix(JunitXmlReporter): resolve paths with irrelevant directories correctly (#3479)
  • Fix Codepoint.ascii() to return arbitrary printable ASCII characters (#3429)
  • Fixing BOM publication to include -jvm artifacts. Fixes #3417
  • Re-implement language injection annotation (#3397)
  • Support UUID, Path, file as stable identifier on JVM (#3472)


  • Upgrade to Kotlin 1.8 (#3468)
  • Adding generators for upper/lower casing strings (#3402)
  • expose random seed in property context (#3469)
  • Printing type when failing numeric or default comparison (#3395)
  • Add access to background scope via extension (#3315)
  • 'assertSoftly' and 'all' imply clue (#3425)
  • enhance Json assertions reuseability (#3438)
  • Add shouldContainAllIgnoringFields (#3394)
  • Expose discovered specs as TestDescriptors during discovery and add support for unique IDs (#3461)
  • Support superclass annotations when deciding whether a class should be isolated. (#3441)
  • Deprecate older json matchers (#3474)
  • Move constant now to new module; bump junit to 1.8.2 (#3470)
  • Added @RequiresPlatform (#3475)
  • Added shouldBeEqual (#3477)
  • Expose testCoroutineScheduler to mpp (#3471)
  • Implement shouldThrowSoftly (#3476)
  • Added Exhaustive for permutations of a list (#3473)
  • shouldBe/shouldNotBe chain (#3186)
  • Tags defined in spec should be applied before listeners (#3189)
  • use GlobalArbResolver for reflective Arbs (#3455)
  • property arb for duration (#3227)
  • add edgecase 'emptyMap' to (#3447)
  • Restoring old mocha/jasmine external test functions
  • Remove concurrency mode from docs (#3434)
  • Adding tvos sim / watchos sim snapshot deployments
  • Increase max arity of checkall property tests to 22 (#3382)
  • Support coroutineTestScope globally (#3383)

Thank you to all the contributors since the 5.5.0 release:

  • Alex Decker
  • Alexey Genus
  • Alphonse Bendt
  • Andrey Kozlov
  • AnouarD
  • Anouar Doukkali
  • Arvind Arikatla
  • aSemy
  • Bartłomiej Zaręba
  • eduardbosch-jt
  • Emil Kantis
  • Grégory Lureau
  • Ivan “CLOVIS” Canet
  • IvanPavlov1995
  • Jama Mohamed
  • Jean-Michel Fayard
  • julian abiodun
  • Julian K
  • Leonardo Colman Lopes
  • Łukasz Pięta
  • Marc Philipp
  • Martin Caslavsky
  • Matej Drobnič
  • Mitchell Yuwono
  • OliverO2
  • Osip Fatkullin
  • ov7a
  • Pankaj
  • Ryan Lewis
  • RyuNen344
  • Sangboak Lee
  • Sergey Volkov
  • Shervinox
  • sksamuel
  • Stefanqn
  • Travis
  • Varun Arora
  • Vinícius Hashimoto
  • Vladimir Sitnikov
  • Xavier Oliver
  • Zak Henry

5.5.5 February 2023

  • Support coroutineTestScope globally (#3383)
  • Improved double and float tolerance messages (#3355)
  • Nested Data Driven Tests is not displayed as nested in Intellij #3341
  • Fixed writing seeds when test name contains a colon on windows (#3304)
  • withClue() fails with EmptyStackException if a coroutine switches threads #2447
  • Use TestDispatcher inside beforeInvocation callbacks (#3363)
  • Make checkCoverage checking against provided pairs (#3344)
  • Kotest runner junit5 jvm has vulnerable transative dependency CVE-2021-29425 #3364
  • Fix sequence matchers for constrained sequences (#3336)
  • Print full path in JunitXmlReporter when useTestPathAsName is enabled instead of just leaf and first parent #3347
  • Support { } lambdas as lazy clues (#3348)
  • Use 'language injection' on assertions, so embedded languages are easier to use in IntelliJ #2916
  • Removing default location for htmlReporter and using the default value from the constructor (#3306)
  • Arb.bigDecimal should generate decimals which terminate with all kinds of terminal digit #3282
  • Check enums using equals method instead of scanning their properties (#3291)
  • Add BlockHound support (#3308)
  • Matchers return this. (#2945)
  • Added shouldMatchResource, shouldNotMatchResource matchers (#2945)
  • Added matchExactly matcher for Maps #3246
  • Fix dumping config when systemProperty set to true (#3275)
  • Returning the original failure when ErrorCollector has only collected a single failure (#3269)

5.5.4 November 2022

  • Fixes an issue when combining gradle filters. (AND was wrongly applied between filters, instead of OR) (#3277)

5.5.3 October 2022

  • Updated JUnit version from 5.7.2 to 5.8.2.

Kotest now requires the runtime version of JUnit to be at least 5.8.x

Note: If your build somehow manages to put both JUnit 5.7 and 5.8 onto the classpath and they load in the wrong order, you might see problems related to ClassOrderer not being found. Please make sure that only JUnit 5.8+ is loaded

5.5.2 October 2022

  • Gradle test filter fixes, by @myuwono (#3257)
  • Tag inheritance configuration is now available on AbstractProjectConfig

5.5.1 October 2022

  • Fixed an issue where tests where being skipped when filtered out by the full spec name

5.5.0 October 2022


  • Fix issue using compiler plugin with Kotlin 1.7.20. (#3220)
  • Allow registering global custom arbs through GlobalArbResolver (#3185)
  • Fix data tests for all BehaviorSpec scopes. (#3222)
  • Fix nullable maps in data tests (#3218)
  • Detect project config after applying config from system properties (#3204)
  • Support enabledOrReasonIf in nested FunSpec
  • Fix misleading error message when Arb.of is given an empty list (#3195)
  • Error if trying to use afterEach callback after test registration (#3191)
  • Attempt to improve the error message for containExactly when used with non-stable sets (#3194)
  • Wrap InvalidPathException into an AssertionError when attempting to use invalid json path (#3147)


  • Added lazy mountable extensions (#3187)
  • Support printing unsigned integers clearly (#3149)
  • Added shouldBeCloseTo matcher (#3181)
  • Added new regex matchers: shouldMatch, shouldMatchAll, shouldMatchAny
  • Wildcard support in launcher (#3200)
  • Support test coroutines on K/N (#3219)
  • Add ability to toggle the inheritance of @Tags (#3199)
  • Publish Gradle version catalog (#3171)
  • Support prefix wildcards in gradle --test selectors (#3190)
  • Better unique collection matchers (#3188)
  • Add cartesian triples helpers for Exhaustive (#3174)
  • use configurable property for Kotest compiler plugin version (#3168)
  • Support printing unsigned integers clearly (#3149)

Thanks to all the contributors since the 5.4.0 release:

  • Alex
  • aSemy
  • ataronet
  • Charles Korn
  • Emil Kantis
  • Jaehyun Park
  • James Baker
  • Jinseong Hwang
  • Kevin Woodland
  • Leonardo Colman
  • Michael Sewell
  • Mitchell Yuwono
  • Nikunj Yadav
  • Prat
  • Rasmus V. Plauborg
  • sksamuel
  • YongJoon Kim

5.4.2 August 2022

  • Fix issues running tests for native targets on Kotlin 1.7+ (#3107)
  • shouldContainJsonKey should be true for keys with null values (#3128)

5.4.1 July 2022


  • Fix regression which causes NoSuchMethodError when using the Kotest Spring extension

5.4.0 July 2022


  • Fix problem with isolation mode when duplicate names occur (#3071)
  • Allow Arb.bind to directly bind to sealed, enum and private types (#3072)
  • Fix to apply before tests #3087
  • Fix shouldHaveSameContentAs doesn't close the readers (#3091
  • Fix tolerance matchers for negative values. (#3096)
  • Adjust warning message to match enum value (#3067)
  • Fix compilation failures for Kotlin/Native projects that use Kotlin 1.7 and the Kotest Gradle plugin. (#3073)
  • Fix description of harryPotterCharacter arb (#2963)


  • Support persisting and reusing seeds for property tests #2967
  • shouldMatchAll has been added to Maps where each value is a function containing assertions. #3065
  • shouldBeEqualToComparingFields now supports configuring classes which require the use of shouldBe for equality, over regular equals
  • Add arbs for ZoneId, ZonedDateTime, and OffsetDateTime (#3113)
  • YearMonth Arbitrary implementation (#2928)
  • Make arb.orNull provide a shrink to null (#2975)
  • Enable building native targets for kotest-assertions-json. (#3021)
  • Json Array size validation (#2974)
  • Add optional reason to @Ignored (#3030)
  • Set runtime retention on dsl marker (#3038)
  • Add shrinker for Sets (#3045)

Experimental features and changes

  • Assumptions have been added to property testing.
  • Statistics generation has been added to property testing.
  • JSON schema array assertions now support minItems, maxItems and uniqueItems #3026
  • (BREAKING) Altered the contract of JSON schema DSL to default to required properties, required has been changed to optional, with false as default.


  • Deprecated existing shouldBeEqualToComparingFields in favor of a new shouldBeEqualToComparingFields matcher which lets you configure the behaviour using a FieldsEqualityCheckConfig class. (#3034)

Thanks to all contributors since the 5.3.0 release:

  • Alphonse Bendt
  • Andrey Bozhko
  • aSemy
  • Ashish Kumar Joy
  • blzsaa
  • Charles Korn
  • Cory Thomas
  • Emil Kantis
  • Erik Price
  • Francesco Feltrinelli
  • Javier Segovia Córdoba
  • Jim Schneidereit
  • Jordi
  • Norbert Nowak
  • Roland Müller
  • Shervinox
  • sksamuel
  • Tim van Heugten
  • YongJoon Kim
  • Zvika

5.3.2 June 2022


  • Fixes compiler plugin issue with Kotlin/Native using Kotlin 1.7, issue #3060

5.3.1 June 2022


  • Support for Kotlin 1.7

5.3.0 May 2022


  • Fail fast should nest to any level #2773
  • Fix Repeating Container Descriptions Break the Execution #2884
  • Fix JS code generation for 1.6.21 by using main (#2947)
  • AbstractProjectConfig is missing displayFullTestPath #2941


  • Support gradle class method filters (#2954)
  • Offer coroutines runTest mode (#2950)
  • Added sortedBy matcher (#2944)
  • Automatic binding of enums. Closes #2937
  • Make it easier to configure options through environment variables by also supporting variable names with underscores instead of dots. (#2925)
  • EndsWith and startsWith matcher support regex for (#2892)

Thanks to all the contributors since the 5.2.0 release:

  • Ashish Kumar Joy
  • Charles Korn
  • coffee-and-tea
  • dependabot[bot]
  • Emil Kantis
  • Goooler
  • Imran Malic Settuba
  • Jim Schneidereit
  • Łukasz Pięta
  • Marcin Zajączkowski
  • Michał Gutowski
  • Mitchell Yuwono
  • Naveen
  • Niklas Lochschmidt
  • Norbert Nowak
  • Rüdiger Schulz
  • sksamuel
  • Vitor Hugo Schwaab

5.2.3 April 2022


  • Update to fix error with kotlinx-coroutines 1.6.1 (#2912)
  • Fixes haveElementAt Matcher throw ArrayIndexOutOfBoundsException (#2895)

5.2.2 March 2022


  • Adjust PIT gradle plugin configuration (#2903)
  • implement trampolines for flatmap, map, filter, merge. (#2900)
  • fix to honor minSize parameter in both generation and shrinks (#2890)
  • Made isOrderedSet platform-specific, to allow TreeSet eq. Fixes #2879
  • Fix negativeFloat and positiveFloat edgecases (#2880) Mitchell Yuwono* 16 Mar 2022, 21:56 b40de793
  • Fixes shouldBeEqualToComparingFields failure when nested field contains null (#2874)


  • Implement ShouldThrowWithMessage (#2847)
  • Implement CharSequence Inspectors (#2886)

5.2.1 March 2022


  • Fixes a regression in 5.2.0 which introduced an error when trying to access root scope from test scope.
  • Trying to define root tests during execution of nested tests now errors correctly. (2870)

5.2.0 March 2022


  • AnnotationSpec does not support suspend @Before function (2868)
  • Fixed dependency scope for RgxGen in property tests (2800)
  • BigDecimal arb could return edgecases outside min max limits (2834)
  • Fix random spec sorter creating invalid comparator (2840)
  • Fix withClue and assertSoftly interference with concurrent coroutines (2791)
  • Fix handling the edge cases of lenient json number comparison (2793)
  • Corrects group id for kotest assertion compiler module. (2787)
  • Add workaround for issue where no tests are run when using new Kotlin/Native memory model. (2812)

Features and improvements

  • Added forSingle inspector and matchEach, matchInOrder and matchInOrderSubset matchers (2695)
  • Added shouldBeJsonObject and shouldBeJsonArray matchers (2861)
  • Ignore JUnit UniqueId selectors for better interop with other engines (2862)
  • Easily compose matchers together (2864)
  • Make length of collection snippet included in assertion errors configurable (2836)
  • Smart cast shouldBeSuccess and shouldBeFailure (2853)
  • Remove inconsistent exceptionClass default values in eventually (2831)
  • Makes shouldBeEqualToComparingFields recursive (2833)
  • Add blockingTest to the config options on FreeSpec 2805 (2807)
  • Added EqualsVerifier contract for shouldBeEqualTo for greater customization (2795)
  • Add containExactly that takes a vararg of pairs (2781)
  • Update Test Containers to support multiple init scripts (2811)

Breaking Changes

  • Disallow use of root scope methods inside container scope (2870)

Thanks to all the contributors:

  • Ashish Kumar Joy
  • BjornvdLaan
  • Charles Korn
  • Christoph Sturm
  • Emil Kantis
  • Imran Malic Settuba
  • Ing. Jan Kaláb
  • inquiribus
  • Kacper Lamparski
  • KIDANI Akito
  • Leonardo Colman
  • Louis CAD
  • Łukasz Pięta
  • luozejiaqun
  • Mervyn McCreight
  • Mitchell Yuwono
  • OliverO2
  • scottdfedorov
  • Sebastian Schuberth
  • sksamuel
  • Sondre Lefsaker
  • Sunny Pelletier
  • Zak Henry

5.1.0 January 2022


  • Test fails because lhs of shouldBe is List, and rhs is a home-grown Iterable #2746
  • JUnit XML extension generates invalid XML #2756
  • Non-nullability gets lost with shouldBeSuccess matcher #2759
  • Arb.bind should detect nullables and inject null values #2774

Features and improvements

  • Update coroutines to 1.6 final #2768
  • Arb.string shrinking simplest character is always 'a' regardless of codepoint #2646
  • Add mutable test clock #2655
  • Inspectors for maps #2656
  • Add conditional invert function with parameter to conditionally invert #2658
  • Add project wide fail fast #2684
  • Allow setting the seed used for randomizing spec order #2698
  • Option to fail build if a seed is set on a property test #2701
  • LocalDateTime arb should accept localdatetimes as min and max #2704
  • System property to disable config scanning #2766
  • System property for config class #2767

Thanks to all the contributors:

  • aSemy
  • Ashish Kumar Joy
  • Bart van Helvert
  • Benjamin Shults
  • Charles Korn
  • Emil Kantis
  • Imran Settuba
  • inquiribus
  • Łukasz Pięta
  • Max Rumpf
  • Ricardo Veguilla
  • Sebastian Schuberth
  • Simon Vergauwen
  • sksamuel

5.0.3 December 2021


  • ShouldContainExactlyTest fails on Windows because of path separators assertions bug #2732
  • shouldBe goes into an infinite loop when generating diff message for data class with cyclic references #2611
  • Issues when using globalAssertSoftly assertions bug framework #2706
  • Fix issues in shouldStartWith and shouldEnd #2736

5.0.2 December 2021


  • Fixed erroneous timeout reporting in tests #2714
  • Team City Listener should not be lazy for all tests #2707
  • Fix Test path filter vs whitespace in test names #2725
  • Support nulls in data driven testing #2718
  • Fixes clue not working were expected or actual is null #2720
  • Changed timeout defaults to use durations for clarity
  • Fixed after/before container not being extensions #2721
  • Share TestCoroutineDispatcher in nested tests #2703
  • Fixes FunSpec contexts where tests are disabled #2710
  • Return ComparableMatcherResult from json assertions #2620
  • Remove @ExperimentalTime where Duration has gone stable #2708
  • Remove Arb#long workaround for incorrect randomly generated values #2700

5.0.1 November 2021


  • Display names now include affixes when configured
  • Fixed WordSpec to work with intellij plugin when used nested contexts
  • Added testCoroutineDispatcher override to project config #2693
  • Fixed compiler plugin multiplatform race condition #2687
  • Regression: Test times reported as zero in junit #2686
  • Dump coroutine debug output automatically after test finishes #2680
  • JSON Matchers does not offer "Click to see difference"

4.6.4 November 2021


  • Fixes ShouldContainExactly for collection containing byte arrays (#2360)
  • Fix InstantRange random nanos selection when the seconds equal the ends of the range (#2441)
  • Fix endless recursion in 2-arity checkAll (#2510)
  • Fix wrong index in forAll4 (#2533)
  • Fixes withEnvironment empty system environment variables on Linux (#2615)
  • Change should to shouldNot on shouldNotBeEqualToComparingFieldsExcept (#2637)
  • Remove accidentally nested Try (#2669)

5.0.0 November 2021

Kotlin 1.6 is now the minimum supported version

See detailed post about 5.0 features and changes here

Breaking Changes and removed deprecated methods

  • Javascript support has been reworked to use the IR compiler. 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 test only IR.
  • Arb.values has been removed. This was deprecated in 4.3 in favour of Arb.sample. Any custom arbs that override this method should be updated. Any custom arbs that use the recommended arbitrary builders are not affected. #2277
  • The Engine no longer logs config to the console during start by default. To enable, set the system property kotest.framework.dump.config to true. #2276
  • TextContext has been renamed to TestScope. This is the receiver type used in test lambdas. This change will only affect you if you have custom extension functions that use TestContext.
  • The experimental datatest functions added in 4.5 have moved to a new module kotest-framework-datatest and they have been promoted to stable.
  • equalJson has an added parameter to support the new shouldEqualSpecifiedJson assertion
  • Changed PostInstantiationExtension to be suspendable
  • ConstructorExtension is now JVM only. Previously it was available on other targets but had no effect outside the JVM.
  • When using inspectors, the deprecated kotlintest.assertions.output.max system property has been removed. This was replaced with kotest.assertions.output.max in 4.0.
  • The deprecated isolation setting in Specs has been removed. Use isolationMode.
  • Moved assertionMode from TestCase to test case config.
  • The deprecated RuntimeTagExtension has been undeprecated but moved to a new package.
  • Removed deprecated shouldReceiveWithin and shouldReceiveNoElementsWithin channel matchers.


Test Framework

  • Support composed annotations plus caching of annotation lookups #2279
  • Fix autoClose lazyness #2395
  • Strip . from JS test names #2483
  • Escape colons for team city output #2445
  • Delete temporary directories recursively when using tempdir #2227


  • String matchers now also work on CharSequence where applicable #2278
  • withEnvironment fails with empty system environment variables on Linux #2615
  • Fixes ShouldContainExactly for collection containing byte arrays #2360
  • 2412 Makes Sequence.containExactly work for single pass sequences #2413
  • Fix withClue and assertSoftly for coroutines switching threads #2447
  • Allow clues to be added to timeouts #2230
  • Possible confusion between shouldContainExactlyInAnyOrder overloads #2587
  • shouldBeEqualToComparingFields handles arrays and computed properties #2475

Property Testing

  • Fix Arb.long/ulong producing values outside range #2330
  • Fix Arb.localDate take into account the date/month portion of the specified minDate #2370
  • updated FloatShrinker and DoubleShrinker to regard mantissa bit count as complexity measure #2379
  • Bugfix/2380 arb filter shrinks #2434
  • PropTestConfig's iterations parameter not being respected #2428
  • Fix endless recursion in 2-arity checkAll #2510
  • Fix wrong index in forAll4 #2533
  • StackOverflow when using checkAll #2513
  • fix Arb.uuid performance by caching RgxGen instances for reuse #2479
  • Property Module: Mutation of global PropertyTesting fix for Kotlin/Native #2469
  • Add BigDecimal edge case for equals vs compareTo discrepancy #2403
  • Fix InstantRange random nanos selection when the seconds equal the ends of the range #2441


Test Framework


  • Return the resulting value of the function block from shouldCompleteWithin #2309
  • Added shouldEqualSpecifiedJson to match a JSON structure on a subset of (specified) keys. #2298
  • shouldEqualJson now supports high-precision numbers #2458
  • Added shouldHaveSameStructureAs to file matchers
  • Added shouldHaveSameStructureAndContentAs to file matchers
  • Inspectors are now inline so can now contain suspendable functions #2657
  • String.shouldHaveLengthBetween should accept ranges #2643
  • beOneOf assertion now tells you what the missing value was #2624
  • String matchers have been updated to work with any CharSequence #2278
  • Add shouldThrowMessage matcher #2376
  • Add Percentage tolerance matchers #2404
  • Add NaN matchers to Float #2419
  • Replaced eager matchers with lazy counterpart #2454
  • Compare JSON literals in Strict mode #2464
  • Added matchers for empty json #2543
  • Added comparable matcher result and applied to shouldContainExactly #2559
  • Updated iterables.shouldContain to return the receiver for chaining
  • Added aliases for inspectors #2578
  • Inspectors should return the collection to allow chaining #2588
  • Disable string diff in intellij #1999
  • CompareJsonOptions has been added for more control when comparing json #2520
  • Support for ignoring unknown keys in JSON asserts #2303
  • Add support for Linux ARM64 and macOS ARM64 (Silicon) targets. #2449

Property Testing

  • Change usages of Char.toInt() to Char.code since Kotlin 1.5. Migrate codepoints to Codepoint companion object. #2283
  • Generex has been replaced with Rgxgen #2323
  • Improve Arb function naming #2310
  • Improve Arb.primitive consistency #2299
  • Add Arb.ints zero inclusive variants #2294
  • Add unsigned types for Arb #2290
  • Added arb for ip addresses V4 #2407
  • Added arb for hexidecimal codepoints #2409
  • Added continuation arbs builder that allow arbs to be used in a similar fashion to for comprehensions. #2494
  • Added as an alias for Arb.bind #2644
  • Add primitive arrays to Arb #2301
  • improved geo location generator #2390
  • Fix LocalDate arb generating wrong dates outside constraints #2405
  • Add zip for Exhaustive #2415
  • Add cartesian pairs helpers for Exhaustive #2415
  • Add Arb.distinct that will terminate #2262
  • Add arb for timezone #2421
  • Added auto classifiers #2267
  • Added arity8 and arity9 forall for table testing #2444
  • Allow global seed configuration. Synchronize defaults. #2439
  • Support complex data classes in Arb.bind #2532
  • Shrink when using Arb.bind #2542
  • Introduce constraints for property testing #2492
  • Property testing should use bind as default for data class #2355
  • Platform independent double shrinker #2517
  • Arb.pair should return Arb<Pair<K, V>> #2563
  • Add support for Linux ARM64 and macOS ARM64 (Silicon) targets. #2449


  • CompareMode /CompareOrder for shouldEqualJson has been deprecated in favor of compareJsonOptions { }
  • TestStatus has been deprecated and TestResult reworked to be an ADT. If you were pattern matching on TestResult.status you can now match on the result instance itself.
  • val name inside Listener has been deprecated. This was used so that multiple errors from multiple before/after spec callbacks could appear with customized unique names. The framework now takes care of making sure the names are unique so this val is no longer needed and is now ignored.
  • SpecExtension.intercept(KClass) has been deprecated in favor of SpecRefExtension and SpecExtension.intercept(spec). 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.
  • The global configuration object has been deprecated as the first step to removing this global var. To configure the project, the preferred method remains ProjectConfig, which is detected on all three platforms (JVM, JS and Native).
  • SpecInstantiationListener has been deprecated in favour of InstantiationListener and InstantiationErrorListener, both of which support coroutines in the callbacks. SpecInstantiationListener is a hold-over from before coroutines existed and will be removed in a future version.
  • The listeners method to add listeners to a Spec has been deprecated. When adding listeners to specs directly, you should now prefer fun extensions() rather than fun listeners().
  • SpecIgnoredListner (note the typo) has been renamed to InactiveSpecListener.


Thanks to all authors who contributed to this huge release. In alphabetical order (all commits since 4.6.0)

AJ Alt, Ali Khaleqi Yekta, Alphonse Bendt, Andrew Tasso, Ashish Kumar, Ashish Kumar Joy, Bart van Helvert, Charles Korn, Christoph Pickl, Cory Thomas, dave08, Derek Chen-Becker, dimsuz, Emil Kantis, Federico Aloi, Hugo Martins, IgorTs2004, Imran Settuba, Ing. Jan Kaláb, IvanPavlov1995, Javier Segovia Córdoba, Jean-Michel Fayard, Jerry Preissler, Jim Schneidereit, Leonardo Colman, Marcono1234, Marvin Sielenkemper, Mervyn McCreight, Michael Werner, Mikhail Pogorelov, Mitchell Yuwono, Nico Richard, niqdev, OliverO2, Rustam Musin, Scott Busche, Sebastian Schuberth, Simon Vergauwen, sksamuel, Srki Rakic, SuhyeonPark, Tobie Wee

4.6.3 September 2021


  • StackOverflow when using checkAll with certain arity functions #2513
  • Added arity8 and arity9 forall for table testing #2444

4.6.2 August 2021


  • Reverted use of 1.5 API introduced erroneously in 4.6.1
  • autoClose breaks lazy #2388
  • minDate not respected in Arb.localDate #2369
  • Sequence.containExactly should work for single pass sequences #2412
  • BigDecimal edge case for equals vs compareTo discrepancy #2403
  • PropTestConfig's iterations parameter is not respected. #2428
  • tempfile and tempdir should fail test when deletion fails #2351

4.6.1 July 2021


  • HTMLReporter - css not loading (href of the file is absolute, not relative) #2342
  • Annotations such as @Ignore and @Isolate now work when composed #2279
  • Finalize spec is now properly called in all situations #2272
  • Arb.bigDecimal bounds are not being honored #2357
  • Fix for running individual test using WordSpec inside intellij #2319

4.6.0 May 2021

This is a small release which adds support for Kotlin 1.5 while remaining compatible with Kotlin 1.4.x


  • All internal logging now uses lazy functions which offers a significant speed up on large test suites. Thanks to Łukasz Wasylkowski who spent considerable time tracking down this performance issue.
  • Fixed false negative results by Inspectors when used inside assertSoftly. #2245

Features / Improvement

  • Test config can now be specified at the test container level in addition to the leaf level #1370 #2050 #2065
  • In data driven tests, added IsStableType annotation which when use on a type, kotest will call toString method on that type for creating test name. See updated docs #2248
  • In data driven tests, added WithDataTestName interface which allow a type to modify the test name generated. See updated docs #2248
  • Reflection methods are cached to avoid slow reflection calls.
  • Added experimental versions of eventually, until, and continually that don't use kotlin.time internally. See updated docs #2149
  • Coroutines upgraded to 1.5 which also allows us to release assertions/property tests for watchosX64
  • WatchosX64 artifacts released for assertions and property tests.


Ashish Kumar Joy, Jim Schneidereit, Łukasz Wasylkowski, sksamuel

4.5.0 May 2021

As part of this release, third party extensions were promoted to top level repositories instead of modules inside the main kotest repo. This allows the extensions to iterate quickly, without needing to wait for a full Kotest release.

From 4.5 onwards, the namespace for all extensions has changed to io.kotest.extensions and the versioning reset to 1.0.0.

So, for example, if you used the Spring extension, you would previously have added io.kotest:kotest-extensions-spring:4.x.y to your build. Now you would use io.kotest.extensions:kotest-extensions-spring:1.x.y

See the full list of extension modules.

Breaking Changes

  • In order to use ExperimentalKotest more broadly, it was moved from io.kotest.core.config.ExperimentalKotest to io.kotest.common.ExperimentalKotest. #1950
  • In order to ensure the EventuallyListener is called in eventually when an exception is thrown the ListenerState field result was changed from type T to type T?. This will allow insight into when the eventually producer function is failing for whatever reason instead of appearing as if it is hanging. #2190
  • Property tests now randomly cycle between edge cases and samples, rather than iterating all edge cases first. This allows greater number of edge cases to be used and avoids a combinatoral explosion. If you are implementing custom Arb's by extending the Arb class (instead of using the arbitrary builders), then you will need to adjust your edge cases method from fun edgecases(): List<A> to fun edgecase(rs: RandomSource): A?.
  • Because of the above property test change, if you are setting a seed in a property test you may need to adjust the value.
  • The kotlin stdlib dependencies are now marked as compileOnly, meaning the version in your build will be used. Kotest tries to maintain compatibility across multiple versions by not relying on features only available in the latest releases.
  • Duplicated test names no longer throw an automatic error, but now mangle the name. So two tests of name 'foo' will appear as 'foo' and '(1) foo'. This enables data driven testing to work properly in javascript. To restore the original behavior, set the configuration value Configuration.duplicateTestNameMode = Error.

Features / Improvement

  • A new data testing module has been added kotest-framework-datatest which properly supports runtime nesting of data tests. See updated docs #2078
  • Added new matcher for DayOfWeek in kotest-assertion-clock module. #2124
  • Added factory method to simplify creating new matchers. #2122
  • Added method in Exhaustive to create a new Exhaustive which will be a cartesian product of given two Exhaustive. #2120
  • Added support for writing tests inside an object as well as class. #1970
  • Added suspend version of shouldCompleteWithin, shouldCompleteBetween and shouldTimeOut. #2107
  • Added kotest-extensions-wiremock project for managing lifecycle of WireMockServer in Kotest test. #2108
  • Added kotest-extensions-kafka project for using embedded kafka in your tests
  • Upgrade klock dependency to 2.0.6 and added browser, nodejs, linuxX64, mingwX64, macosX64, tvos, iosX64, iosArm64 and iosArm32 platform targets for kotest-assertions-klock. #2116
  • Run eventually one final time if iterations is one and delay is greater than the interval #2105
  • Some improvement around eventually.
    (1) Makes EventuallyPredicate a type alias instead of interface for better user experience.
    (2) Update failure message to inform the user about failure of given EventuallyPredicate.
    (3) Adds an overload of eventually which does not accept EventuallyPredicate so that it gives a feel of until function.
  • Added shouldBeEqualToComparingFields and shouldBeEqualToComparingFieldsExcept matchers which check equality of actual and expected by comparing their fields instead of using equals method. #2197
  • one and any have been added as alternatives to assertSoftly. These are suspending methods that will check that only a single assertion succeeded (in the case of one) or that at least one assertion succeeded (in the case of any). #1950
  • New reporter added to generate HTML reports #2011
  • Exhaustive.cartesian has been added #2119
  • kotest.tags can now be set via ENV Vars #2098
  • Edgecases are now probabilistic based #2112
  • TestResult should support a reason why tests were skipped #2172
  • Add watchos support back for x86 #2204
  • Add overload to Double.plusOrMinus that accepts a percentage value instead of an absolute one. 1.0.plusOrMinus(10.percent)


  • Fixes eventually failing inside assert softly block without retrying the given lambda. #2092
  • Fixes any other implementation of Listener apart from ProjectListener not getting picked by Kotest framework. #2088
  • Fixes EventuallyListener not being called in eventually when the producer function throws an exception. #2190
  • Use the classname as the default prefix for temporary files #2140
  • Fix for SystemExitListener and picocli framework #2156
  • Fix for Arb.choose(arb, arb2, ...) not generating random values #2176
  • Using checkAll, forAll and using take on an Arb cause an InvalidMutabilityException on XorWowRandom for Ios #2198
  • Fix issues of passing vararg to another function in containsInOrder #2200
  • The StringShrinker ignored min size limit #2213
  • Fix for unlimited concurrency in spec execution when using experimental concurrency support #2177
  • Synchronize access to Spring test contexts #2166
  • Fixed typo in haveClassAnnontations matcher. Existing incorrect spelling is deprecated. #2133


  • Deprecated instanceOf, beInstanceOf, beTheSameInstanceAs, beOfType of package io.kotest.matchers these will be removed permanently in 4.7 release, you can import these same assertion from io.kotest.matchers.types package.
  • Remove deprecated eventually that uses durations for intervals. #2086
  • Receivers used in test scopes have been renamed. For example, DescribeScope has become DescribeSpecContainerContext. The previous names exist as typealiases but are deprecated. This is only of importance if you implement custom spec types that inherit from the builtin specs or have defined extension methods on those scopes.


  • AJ Alt
  • Alex Ordóñez
  • Andreas Deininger
  • Ashish Kumar Joy
  • Dale King
  • Hirotaka Kawata
  • Hugo Martins
  • Janek
  • Jim Schneidereit
  • Leonardo Colman
  • Malte Esch
  • Mateusz Kwieciński
  • Mitchell Yuwono
  • Nikita Klimenko
  • Niklas Lochschmidt
  • Rustam Musin
  • Sean Flanigan
  • Sebastian Schuberth
  • Yoonho Sean Lee
  • Zak Henry
  • sksamuel
  • tbcs

4.4.3 March 2021

  • Removed verbose debugging statements that were erroneously left in the 4.4.2 release.

4.4.2 March 2021

Note: Release 4.4.2 is compiled against Kotlin 1.4.31 and coroutines 1.4.3

  • Feature: The Javascript test artifacts are now compiled against the IR compiler in addition to current #2037
  • Bugfix: BeforeProjectListener was not always being detected
  • Bugfix: Using shouldBe with throwables would compare using the message only #2094
  • Bugfix: Fix withEnvironment() to be case-insensitve on Windows #2099
  • Bugfix: Fix IncorrectDereferenceException when calling assertions on background thread on native #2128
  • Bugfix: Fix Arb.bigdecimal hanging for some combinations of min and maxvalues #2135
  • Improvement: eventually sometimes only checks a single time despite short scheduled intervals #2089
  • Improvement: Updates error message for shouldContainKeys matcher to includes keys which are not present in given map #2106
  • Improvement: haveCauseOfType shows exception type instead of cause type #2131

4.4.1 February 2021

Note: Release 4.4.1 bumps the minimum required version of Kotlin to 1.4.30

  • Fixed allure test grouping #1871
  • Updated shouldBeEmpty and shouldNotBeEmpty to work for nullable references #2055
  • Expose factor in exponential interval in eventually and until #2046
  • Added cap to exponential and fibonacci intervals #2053
  • Fix test name for data driven test when data class contains enum values #2034
  • IntArray not being printed in Assert log #2042
  • Fixed invalid json causing streaming error in json assertions #2045
  • Generation of larger sets via Arb.set throws an exception #2051
  • Avoid creating extra lambdas in blocking forAll #2036

4.4.0 February 2021

Note: Release 4.4.0 bumps the minimum required version of Kotlin to 1.4.21

Features / Improvements

  • Add lazy property test generator #1651
  • New map assertions #1697
  • Property test framework is now deployed for native targets #1747
  • Improve concurrency support for specs / tests #1760
  • Variation of clue / asClue to accept lazy #1766
  • New Map assertions shouldNotContainAnyKeysOf() shouldNotContainAnyValuesOf() #1769
  • Add matchers for Atomic Booleans #1791
  • Upgrade to Kotlin 1.4.20 #1800
  • Test cases should have their tags appended to the test name if so configured #1804
  • Add functionality to use 'it' without surrounding 'describe' #1827
  • Added inline version for intanceOf alias #1838
  • Add Support for globalAssertSoftly from System Property #1843
  • Helper for temporary directory creation #1862
  • shouldBeBetween not defined for floats #1927
  • Increase arity of checkall / forall property tests to 12 #1929
  • Add more configurations to Email Generator #1941
  • not null matcher should show the value that was meant to be not null #1942
  • Add SpringTestExtension which exposes test context via coroutine context element #1956
  • Add active test extension #1959
  • Upgrade ktor matchers to use ktor 1.5 #1965
  • Allow data driven tests to register in root scope #1967
  • Add domain arbitrary #1969
  • Upgrade arrow matchers to 0.11.0 #1976
  • Add alphanumeric codepoint arb #1989


  • Performance improvements for Exceptions on the JVM #1787
  • Using a symbol or Japanese etc in the test name will change the behavior #1828
  • Wrong behavior when combining assertSoftly and shouldNotBe #1831
  • BehaviorSpec Then assertion shows green in Intellij but should show red #1857
  • AssertionMode.Error doesn't work on FeatureSpec #1864
  • Invalid test usage should throw at runtime #1882
  • Output from reporters should be single threaded #1895
  • Arb.set with a range hangs the test if the given gen inside the set cannot produce enough values for the range #1931

4.3.2 December 2020


  • Assertions library now released for watchos32 in addition to all other targets
  • Allow using it for creating test outside of describe block
  • Added Arb.lazy and Exhaustive.lazy


  • A Kotlin 1.4 specific method was added in 4.3.1 and reverted in 4.3.2
  • Arb.choose does not currently include edge cases from input arbs #1886
  • String shrinking is not being executed #1860
  • Arb.stringPattern slows down the test dramatically #1878
  • AssertionMode.Error doesn't work on FeatureSpec #1864
  • Incomplete edge cases with the double generator #1869
  • Unexpected ToleranceMatcher behavior at infinite doubles #1832
  • Wrong behavior when combining assertSoftly and shouldNotBe #1831
  • Fixed shouldContainJsonKeyValue to work with Long expected value and integer actual value #1790

4.3.1 November 2020


  • Variation of clue / asClue to accept lazy #1766
  • Added Tuple2..Tuple22 for use in data testing #1773


  • Stacktrace recovery when an eventually block fails #1775
  • Performance improvements for Exceptions on the JVM #1787
  • Updated discovery to only initialize spec classes #1788


  • Added stable identifiers when using new data-driven tests with non-data classes #1795
  • Wrong TimeoutException messages shown when test exceeds spec-level invocation timeout #1809
  • Invocation timeouts should not be applied to containers #1810
  • Arb.filter causing stackoverflow #1818
  • Arb.shuffle type signature change broken in 4.3.0 #1824

4.3.0 October 2020 - Blog


  • New data driven test DSL with data classes #1537 (framework)
  • Option to strip whitespace from test names #1545 (framework)
  • EnabledIf annotation for specs #1683 (framework)
  • Propagate coroutine context to tests #1725 (framework)
  • Option to suppress configuration dump #1742 (framework)
  • Added severity attribute for TestCase #1746 (framework)
  • Added kotest.framework.sourceref.disable option (framework)
  • Make Engine dependency free #1748 (framework)
  • Multi-line-string comparison for file contents #823 (assertions)
  • New assertion: Iterator.shouldHaveNext() #1660 (assertions)
  • New assertions: isEmpty / isDefined for java Optional #1661 (assertions)
  • Non infix matchers should return this for easy chaining #1744 (assertions)
  • Add property test module for kotlinx datetime #1679 (prop-testing)
  • Add Gen.forNone #1636 (prop-testing)
  • Arb should generate a single value #1754 (prop-testing)
  • Adds an arbitrary to generate bigdecimal #1705 (prop-testing)
  • Add steps and stack trace to allure, with full docs #460 (extensions)
  • Added roboelectric extension to main build (extensions)

Breaking Changes

  • The kotest-extensions-junit5extensions module is now called kotest-extensions-junit5

4.2.6 October 2020


  • Added per project listener for testcontainers #1731


  • Fixed regression in shouldBe when using iterables/arrays #1707 #1727
  • Fix first failure in beforeTest blocks #1736
  • Deprecate distinct #1730
  • Fixed the empty allure result for tests with the failed afterTest block #1724

4.2.5 September 2020

  • Bugfix: Fixed performance issue when using 1000s of tests in gradle #1693
  • Feature: Added matchers for pair / triple components 1694
  • Feature: Added shouldHaveNameWithoutExtension matcher for files and paths #1696
  • Improvement: Added koin lifecycle mode #1710

4.2.4 September 2020

  • Bugfix: Test time does not scale with number of tests #1685
  • Bugfix: Added spring listener lifecycle mode #1643
  • Bugfix: Fix and remove double negative in empty directory assertions
  • Improvement: Duplicated test name exception should include test name #1686
  • Improvement: SpringListener to generate meaningful method names #1591

4.2.3 September 2020

  • Bugfix: Throwables of Error in the engine should be reported to test engine listeners
  • Bugfix: Switched classgraph to api
  • Bugfix: Make Set comparisons use .contains() instead of a linear search #1672
  • Bugfix: Change retry default delay to 1 #1670
  • Bugfix: removed 1.4 api usage from property tests
  • Improvement: Allow retry to call suspend functions #1669
  • Improvement: Add matcher alias for Iterator have next #1664
  • Improvement: Add java.util.Optional matchers #1662
  • Improvement: Expand ktor matchers to the client libraries #1658
  • Improvement: Add forNone assertion #1654
  • Improvement: Arb and Exhaustive should be covariant #1653
  • Improvement: Remove the annoying executionError extra test in gradle #1655
  • Improvement: Added more helpful error message when spec instantiation fails
  • Docs: Update Gradle dependencies docs removing unnecessary -jvm suffix #1650
  • Docs: MockServer extension documentation #1446

4.2.2 August 2020

  • Bugfix: Usage of a Kotlin 1.4 only method has been removed
  • Bugfix: KotlinReflectionInternalError fixed on java enums #1611
  • Bugfix: Errors in a DiscoveryExtension were not propagated to output #1634
  • Bugfix: Tags specified via inline tags dsl were not being picked up #1642
  • Improvement: Updated output of some collection matchers to format an element per line #1380

4.2.1 August 2020

  • Feature: The assertion libraries are now also published for watchos, tvos, and ios in addition to the macos, windows, and linux targets previously.

4.2.0 August 2020 - Blog

  • Feature: Kotest upgraded to use Kotlin 1.4.0 #1511
  • Feature: Allow multiple project configs to be detected and merged #1632
  • Feature: Allow case control in test's reports #1458
  • Feature: Use expression for tags instead of include/exclude #863
  • Feature: Add new scoped callbacks #1584
  • Feature: Support order annotation for SpecOrder #1593
  • Feature: Spec level overrides for timeout and invocation timeout #1551
  • Improvement: Added exhaustive only mode to property tests #1596
  • Improvement: Change instance of matchers to use generic contracts #1510
  • Improvement: Allow to disable SpringListener on final class warning #1573
  • Improvement: Bundle console runner with intellij plugin #1567
  • Improvement: Improved error message for map should contain when key present #1587
  • Improvement: Allow allure to be customizable #1527
  • Improvement: Use the SPDX compliant license identifier "Apache-2.0" in POM files #1517
  • Improvement: Use forAll(1) suspend parameters #1626
  • Bugfix: Running all tests in a package doesn't run tests in subpackages #1621
  • Bugfix: Can't run a single test method from Gradle 6.5 #1531
  • Bugfix: TestFactory listeners not executing on nested tests #1613
  • Bugfix: Disabling test execution with x-methods doesn't work with kotest-core-js #1623
  • Bugfix: NoSuchFileException when using kotest-extensions-junitxml with Gradle #1581
  • Bugfix: Non complete junit report when using FunSpec #999
  • Breaking Change: kotest-core module has been replaced with kotest-framework-api and kotest-framework-engine. Tools authors can depend on api only. Engine should be used for JS testing. For JVM testing, continue to use kotest-runner-junit5-jvm.

4.1.2 July 2020

  • Bugfix: Dkotest.tags.include= only takes into account @Tags #1536 sksamuel
  • Bugfix: Ensure exhaustive isn't build with an empty list #1549 Cleidiano Oliveira
  • Bugfix: Add concurrent spec runner and fix sequential spec runner #1547 sksamuel
  • Bugfix: Take into account range for IntShrinker and LongShrinker #1535 sksamuel
  • Feature: Support expressions for tags as an alternative to include/exclude #863 sksamuel
  • Feature: Expand some matchers to Iterable #1538 Leonardo Colman Lopes
  • Improvement: Add the ability to make parameter substitutions when executing http files #1560 Shane Lathrop
  • Improvement: Added xGiven / xWhen / xThen options to Behavior spec #1534 sksamuel
  • Improvement: Added nicer syntax for Test Containers sksamuel
  • Improvement: Restore context to describe #1565 sksamuel
  • Breaking Change: Updates method signature of assertSoftly to take object under test as argument Ashish Kumar Joy

4.1.1 June 2020

  • Bugfix: Issue with describe spec and the intellij plugin fixed #1528
  • Bugfix: Incorrect error message with Exhaustive's when under the min iteration count #1526

4.1.0 June 2020 - Blog

  • Feature: The Kotest IntelliJ plugin has gone final. The plugin requires 4.1. or higher of Kotest.
  • Feature: Highlight diff when comparing data classes #826 #1242
  • Feature: Improve error message in tolerance matchers #1230
  • Feature: Add Arb for (lat, long) #1304
  • Feature: Integration with Testcontainers #1353
  • Feature: x variants for Behavior / Feature / Expect spec #1383
  • Feature: Add property test global config with before / after prop test callbacks #1435
  • Feature: Parallel execution test cases in Spec #1362
  • Feature: Add variable.assertSoftly #1427
  • Feature: Coroutine helper for timeout #1447
  • Feature: Add timeout to apply to individual tests when invocations > 1 #1442
  • Feature: Add shouldExistInOrder matcher #1460
  • Feature: Added Arb.orNull #1414
  • Feature: Provide a way to remove test prefixes in the test output when using specs which use prefixes #1486
  • Feature: Adds shouldCompleteExceptionallyWith matcher #1454
  • Feature: Exhaustive.merge for two gens with a common supertype #1502
  • Improvement: Added Byte.shouldBeBetween(min, max) and Arb.bytes #1408
  • Improvement: Remove kotlintest aliases #1457
  • Improvement: Parent scopes are not coroutine scopes #1488
  • Improvement: isolation instead of isolationMode #1418
  • Improvement: Reflection equality improvements #1413
  • Improvement: Property tests should report exception of running shrunk input #1279
  • Improvement: Make beforeProject and afterProject as suspend function #1461
  • Improvement: Updated arb flat map to accept lists #1500
  • Improvement: Date generators should allow for specific dates to be selected #1354
  • Bugfix: Test cases with multiline names broken #1441
  • Bugfix: Before\AfterProject catch only one Exception #1387
  • Bugfix: Arb.bind() calls the incorrect constructor #1487
  • Bugfix: Project config dump doesn't include enums properly #1379
  • Bugfix: Add Arb.choose that accepts weighted arbs #1499
  • Bugfix: Arb.list doesn't use ListShrinker #1493

4.0.6 June 2020

  • Bugfix: Dependencies of assertions-core are now included properly when not using junit runner #1425
  • Bugfix: checkAll would fail if exhaustive size was very large #1456
  • Bugfix: Show typeclass on java.nio.filePath would cause stack overflow #1313

4.0.5 April 2020

  • Bugfix: Focus mode would cause some nested tests to be ignored #1376
  • Bugfix: Arb.choice would include edge cases in the generated values #1406
  • Bugfix: and Arb.long edge cases included values outside the specified ranged #1405

4.0.4 April 2020

  • Bugfix: Exceptions of type LinkageError, most commonly ExceptionInInitializerError were not being handled #1381

4.0.3 April 2020

  • Feature: Koin support now works for koin 2.1 #1357
  • Deprecation: String context is deprecated in ShouldSpec in favour of a context block. #1356
  • Improvement: Line breaks added to Collection.containExactly matcher #1380
  • Improvement: Tolerance matcher emits better failure message (including plus/minus values) #1230
  • Bugfix: Project config output now writes the correct values of test ordering and isolation mode #1379
  • Bugfix: Order of autoclose is restored to work like 3.4.x (was undefined in 4.0.x) #1384
  • Bugfix: Fix shouldContainExactly for arrays #1364

4.0.2 April 2020

  • Feature: Added filter and map to Exhaustives #1343
  • Feature: shouldBeInteger matcher using contracts #1315
  • Bugfix: Fixed issue with xdescribe in describe spec always being active
  • Bugfix: Simple tags were using full class names rather than the simple name breaking backwards compatibility #1346
  • Improvement: Caching result of discovery for increased performance in maven #1325
  • Bugfix: Closing resources used in classgraph scan #1323
  • Bugfix: Fixed timeout for coroutine launched inside a test without its own scope #1345
  • Bugfix: Fix Arb.bind returning only the same value #1348
  • Bugfix: Restored usage of opentest4j assertions #1339
  • Bugfix: Fixed missing stacktrace in data driven testing #1336
  • Bugfix: Fixed Arb.instant always returning same value #1322
  • Bugfix: Added workaround for gradle 5 bugs.

4.0.1 March 2020

  • Improvement: Bumped kotlin to 1.3.71
  • Feature: Aded latlong Arb #1304

4.0.0 March 2020

The 4.0.0 release is a large release. With the project rename, the packages have changed and module names have changed.

Major changes:

  • The KotlinTest project is now multi-platform. This means most of the modules now require -jvm to be added if you are working server side JVM only. For example, io.kotlintest:kotlintest-runner-junit5 is now io.kotest:kotest-runner-junit5-jvm taking into account package name changes and the platform suffix.
  • The main assertions library is now kotest-assertions-core and many new assertions (matchers) have been added. This changelog won't list them all. It is simpler to view the full list.
  • The property test library has moved to a new module kotest-property and been reworked to include many new features. The old property test classes are deprecated and will be removed in a future release.
  • Many new property test generators have been added. The full list is here.
  • Composable specs have been added in the form of Test Factories.
  • Project config no longer requires placing in a special package name, but can be placed anywhere in the classpath.
  • @Autoscan has been added for listeners and extensions.
  • Added DSL version of test lifecycle callbacks.

Minor changes.

  • Feature: A new JSoup assertions module has been added. #1028
  • Feature: Stats matchers #851
  • Feature: Experimental Robolectric Support #926
  • Bugfix: shouldNotThrowAny return T instead of Unit #981
  • Internal: Removed dependency on Arrow to avoid version conflicts
  • Feature: Project wide default test case config
  • Feature: whenReady(f) has been replaced with f.whenReady which is coroutine enabled
  • Feature: Alphabetic test case ordering
  • Feature: All test callbacks are now coroutine enabled
  • Feature: forEachAsClue
  • Improvement: Support Koin 2.1.0
  • Improvement: Explicitly allow internal classes as specs
  • Feature: Klock matcher support #1214
  • Feature: JDBC matcher support #1221


  • Bugfix: Enhances SpringListener to work correctly with all Spring's Listeners #950


  • Internal: Remove JUnit redeclarations #927
  • Feature: Add infix modifier to more Arrow matchers #921
  • Feature: BigDecimal range matchers #932
  • Feature: monotonically/strictly increasing/decreasing matcher #850
  • Feature: Fixes shouldBe and shouldNotBe comparison #913
  • Feature: Add overload to Ktor shouldHaveStatus matcher #914
  • Feature: Fail parent tests when child tests fail #935


  • Feature: Support for running tests with Koin #907
  • Feature: Global timeout option can be applied across all tests #858
  • Feature: Introduced await as a more feature rich version of eventually #888 #793
  • Feature: Array overloads for all matchers #904
  • Feature: Support Spring's Test Listeners #887
  • Feature: Limit Parallelism for some specs #786
  • Feature: Added new project listener #859
  • Feature: Change System extensions to support different modes #843
  • Feature: Print project configurations #841 #866
  • Feature: New date matcher variations for month, time units, day of week, etc #899
  • Feature: Multi line diff min line config option #706
  • Feature: Allow nested describe scope in DescribeSpec #905
  • Feature: Add matcher for Dates to ignore timezone #891
  • Feature: Reflection matchers #614 #894
  • Feature: Added string matchers for single line and size between #853
  • Feature: Added contracts and lambda variations of matchers for arrow types #802 #890 #834
  • Feature: Added matchers for LocalTime #889
  • Feature: Added Zoned and Offset date time variants of shouldBeToday #820
  • Feature: Add new throwable matchers #864
  • Feature: Added matchers for Result #836 #861
  • Feature: Added big decimal matchers #875
  • Feature: Added shouldBeSymbolicLink and shouldHaveParent matchers for files #871
  • Feature: Json Matchers from resources #873
  • Feature: Added shouldBeZero and shouldNotBeZero matcher for number types #819 #848
  • Feature: Added shouldContainFiles matcher for path #854
  • Feature: The URI matchers should also work on URLs. #818
  • Feature: Allow setting isolation mode in project config #842
  • Feature: Added containFileDeep File matcher #846
  • Feature: Implements SkipTestException #805
  • Feature: Implements Infinity and NaN Double Matchers #801
  • Feature: Add asClue helper function #784
  • Feature: Add infix map matchers using Pair #792
  • Feature: Add Short and Btyte primitive gens #773
  • Feature: Implement Gen.take(n) function #758
  • Feature: Implement function #759
  • Feature: Add support to change sizes of generated lists, sets, maps #757
  • Feature: Allow exclusion/inclusion tags at runtime #761
  • Bugfix: Added missing part of shouldHaveLength message #870)
  • Bugfix: Updated json matchers to include actual json in the error
  • Bugfix: Fix for before/after test listeners not failing tests #842 #865
  • Bugfix: Changed autoClose to accept an AutoCloseable #847
  • Bugfix: Fixed left vs right issue #612
  • Bugfix: Ensure specs that fail in initialisation fail a Maven build #832
  • Bugfix: Fixed test engine reporting when there is an exception in either the init block, beforeSpec or the afterSpec method #771
  • Internal: io.kotlintest.Result renamed to io.kotlintest.MatcherResult to avoid conflict with new Kotlin class kotlin.Result #898


  • Feature: Intellij Plugin now available!
  • Feature: FunSpec now allows parent context blocks
  • Feature: java.time between matcher (#694)
  • Feature: Constant 'now' listeners (#693)
  • Feature: PITest plugin (#687)
  • Feature: Spring mocking injection @MockBean @MockkBean (#684)
  • Feature: instanceOf and typeOf matchers to use the casted value (#695)
  • Feature: Digest Matchers #667
  • Feature: continually assertion function #643
  • Feature: Add project config option for assertSoftly #512 (#655)
  • Feature: Implement System Security Manager Extensions (#640)
  • Feature: Implement System Environment Extension (#633)
  • Feature: Implement shouldBeOneOf matcher and assertions (#647)
  • Feature: Add nullability matchers with Kotlin Contracts (#602) (#646)
  • Feature: SystemProperty Test Helpers #524 (#608)
  • Feature: Timezone / Locale Extension #587 (#609)
  • Feature: Move extensions to Kotlintest-Extensions module (#629)
  • Feature: Provide range-based numeric generators and javax.time generators #530 (#543)
  • Feature: Extended word spec (#635)
  • Feature: Implement shouldNotThrow matchers (#603)
  • Improvement: Make "condensed" multi-line diffs configurable #607
  • Improvement: Allow Arrow Either extensions to support nullable types (#613)
  • Improvement: Enables test bang on all specs (#606)
  • Improvement: Add property testing extensions for custom generators (#506)
  • Improvement: Added issue flag in config #525
  • Bugfix: Added support for package selectors from junit discovery requests #597
  • Bugfix: Disabled top level tests are not marked as ignored in JUnit #656
  • Bugfix: Fix containOnlyOnce which return true when no occurrence (#660)
  • Internal: Auto deploy snapshot on each travis build
  • Internal: Remove all deprecated matchers/assertions (#653)


  • Feature: AnnotationSpec now has a expected exception configuration #527 #559
  • Feature: BehaviorSpec gained extra nesting possibilities, with And between any other keywords #562 #593
  • Bugfix: Independent tests were sharing a thread, and one test could timeout a different one for apparently no reason #588 #590
  • Improvement: Documentation on TestConfig.invocations clarified #591 #592


  • Feature: Support for coroutines directly from tests #386
  • Feature: Isolation mode added to more finely control the instances in which tests execute #379
  • Feature: When re-running tests, execute previously failing specs first #388
  • Feature: Support for @Before and @After in AnnotationSpec for easier migration from JUnit #513
  • Feature: Support package selectors in discovery #461
  • Improvement: The test listeners have been reworked to make them more powerful and clearer #494
  • Improvement: Better support for multi-line string comparisions #402
  • Improvement: Gen.oneOf should be covariant #471
  • Improvement: Double should have oppostive matchers for shouldBePositive and shouldBeNegative #435
  • Improvement: New matchers #393 #325
  • Bugfix: BehaviorSpec doesn't allow config bug #495
  • Bugfix: Error when throwing AssertionError from inside a shouldThrow{} block #479
  • Bugfix: Fix test timeouts #476
  • Bugfix: Fix annotation spec failure message #539
  • Internal: Build now uses Kotlin 1.3 #379
  • Internal: Upgraded class scanning to use ClassGraph instead of Reflections #459


  • Feature: Infix support to String matchers #443
  • Feature: Infix support to files, floats, sequences, types and uri matchers #445
  • Feature: Infix support to Double matchers #429
  • Feature: Infix suport to Map matchers #417
  • Feature: shouldNotBePositive and shouldNotBeNegative for Double matchers #435
  • Feature: Support for Duration in time matchers #423
  • Feature: arrow-assertion Failure matcher that checks underlying throwable equality #427
  • Feature: shouldNotBeTrue and shouldNotBeFalse for Boolean matchers #452
  • Improvement: Documentation for #419
  • Improvement: Javadocs for Date matchers #420
  • Improvement: Better error message for empty collection in matchers #438
  • Improvement: Better stacktrace filtering from Failures class #465
  • Bugfix: Double matcher shouldNotBeExactly had the wrong implementation #432
  • Bugfix: Single-thread test had before and after running in separate thread from the test #447
  • Bugfix: Test with invocations > 1 wouldn't complete if test failed #413
  • Bugfix: Wrong assertion on shouldThrow #479 #484


  • Feature: Infix version of some inline matchers, eg date1 shouldHaveSameYearAs date2 (#404 #407 #409)
  • Feature: Infix support for int and long matchers (#400)
  • Feature: Added startsWith/endsWith matchers on collections (#393)
  • Improvement: Use unambiguous representations in collection matchers (#392)
  • Improvement: Collection matchers now work on Sequence too (#391)
  • Improvement: Added shouldThrowUnit variant of shouldThrow (#387)
  • Fix: shouldBe on arrays without static type (#397)


  • Feature: Add soft assertions (#373)
  • Feature: sortedWith (and related) matchers. (#383)
  • Improvement: Removed unnecessary Comparable<T\> upper-bound from sortedWith matchers. (#389)
  • Improvement: Improve StringShrinker algorithm (#377)
  • Bugfix: shouldBeBetween should be shouldBe instead of shouldNotBe (#390)
  • Bugfix: Fix beLeft is comparing against Either.Right instead of Either.Left (#374)
  • Internal: Naming executor services for jmx monitoring


  • Bugfix: Skip tests when MethodSelector is set #367 (means can run a single test in intellij)
  • Bugfix: Fix error when running single test in kotlintest-tests (#371)
  • Bugfix Fix table testing forNone and Double between matcher (#372)
  • Improvement: Remove matcher frames from stacktraces (#369)
  • Improvement: Use less ambiguous string representations in equality errors (#368)
  • Improvement: Improve String equality error messages (#366)
  • Internal: Update kotlin to 1.2.50 (#365)


  • Feature: Added Int/Long.shouldBeNegative and Int/Long.shouldBePositive matchers #325
  • Feature: Added Double.shouldBeNegative and Double.shouldBePositive matchers #325
  • Feature: Added collection.shouldBeLargerThan(c), collection.shouldBeSmallerThan(c), collection.shouldBeSameSizeAs(c) #325
  • Feature: Added collection.shouldHaveAtLeastSize(n) and collection.shouldHaveAtMostSize(n) matchers.
  • Feature: Added matcher for uri.opaque
  • Feature: Add matchers containsExactly and containsExactlyInAnyOrder (#360)
  • Feature: Added test case filters
  • Bugfix: Running single tests with Gradle command line #356
  • Change: Removed coroutine support until it is no longer experimental
  • Improvement: Optimize sorted matcher (#359)
  • Improvement: Allow type matchers to match nullable values. (#358)
  • Improvement: Allow nullable receivers for string matchers. (#352)
  • Improvement: Run tests for all rows in a table, even after errors. (#351)


  • Specs now support co-routines #332
  • Extension function version of inspectors.
  • Inspectors for arrow NonEmptyLists
  • New style of data driven tests with parameter name detection
  • Extension function style of assert all for property testing
  • Updated string matchers to show better error when input is null or empty string
  • Allow nullable arguments to more matcher functions. #350
  • Added extension functions for table tests #349


  • Fix for bug in gradle which doesn't support parallel test events
  • Bring back Duration extension properties #343
  • Added fix for gradle 4.7 issues #336
  • shouldBe does not handle java long #346
  • Fixing function return type in documentation for forAll() (#345)
  • Fixing typos in (#344)
  • Make the Table & Row data classes covariant (#342)
  • Fixing argument names in ReplaceWith of deprecated matchers (#341)


  • Fix eventually nanos conversion (#340)
  • Improve array shouldBe overloads (#339)


  • Added workaround for gradle 4.7/4.8 error #336
  • Fix URI path and URI parameter matchers (#338)


  • Added arrow NonEmptyList isUnique matchers
  • Added Float and List Shrinker
  • Added inspecting and extracting helper functions. (#334)
  • Allow tags to be added to specs for all test cases #333
  • Support randomized order of top level tests #328


  • Focus option for top level tests #329
  • Improve shrinkage #331
  • Updated readme for custom generators #313
  • Added generator for UUIDs
  • Fixed bug with auto-close not being called. Deprecated ProjectExtension in favour of TestListener.
  • Added a couple of edge case matchers to the arrow extension; added arrow matchers for lists.

Version 3.1.0

  • Simplified Setup

In KotlinTest 3.1.x it is sufficient to enable JUnit in the test block of your gradle build instead of using the gradle junit plugin. This step is the same as for any test framework that uses the JUnit Platform.

Assuming you have gradle 4.6 or above, then setup your test block like this:

test {

You can additionally enable extra test logging:

test {
testLogging {
  • Instance Per Test for all Specs

In the 3.0.x train, the ability to allow an instance per test was removed from some spec styles due to implementation difficulties. This has been addressed in 3.1.x and so all spec styles now allow instance per test as in the 2.0.x releases. Note: The default value is false, so tests will use a single shared instance of the spec for all tests unless the isInstancePerTest() function is overridden to return true.

  • Breaking Change: Config Syntax

The syntax for config has now changed. Instead of a function call after the test has been defined, it is now specified after the name of the test.

So, instead of:

"this is a test" {

You would now do:

"this is a test".config(...) {
  • Matchers as extension functions

All matchers can now be used as extension functions. So instead of:

file should exist()


listOf(1, 2) should containNull()

You can do:



listOf(1, 2).shouldContainNull()

Note: The infix style is not deprecated and will be supported in future releases, but the extension function is intended to be the preferred style moving forward as it allows discovery in the IDE.

  • Dozens of new Matchers

even and odd

Tests that an Int is even or odd:

4 should beEven()
3 shouldNot beEven()

3 should beOdd()
4 shouldNot beOdd()


Asserts that an int or long is in the given range:

3 should beInRange(1..10)
4 should beInRange(1..3)


Checks that a collection contains the given element at a specified index:

listOf("a", "b", "c") should haveElementAt(1, "b")
listOf("a", "b", "c") shouldNot haveElementAt(1, "c")

Help out the type inferrer when using nulls:

listOf("a", "b", null) should haveElementAt<String?>(2, null)

readable, writeable, executable and hidden

Tests if a file is readable, writeable, or hidden:

file should beRadable()
file should beWriteable()
file should beExecutable()
file should beHidden()

absolute and relative

Tests if a file's path is relative or absolute.

File("/usr/home/sam") should beAbsolute()
File("spark/bin") should beRelative()


Tests if a file's path begins with the specified prefix:

File("/usr/home/sam") should startWithPath("/usr/home")
File("/usr/home/sam") shouldNot startWithPath("/var")


Asserts that two objects have the same hash code.

obj1 should haveSameHashCodeAs(obj2)
"hello" shouldNot haveSameHashCodeAs("world")


Asserts that two strings have the same length.

"hello" should haveSameLengthAs("world")
"hello" shouldNot haveSameLengthAs("you")

haveScheme, havePort, haveHost, haveParameter, havePath, haveFragment

Matchers for URIs:

val uri = URI.create("https://localhost:443/index.html?q=findme#results")
uri should haveScheme("https")
uri should haveHost("localhost")
uri should havePort(443)
uri should havePath("/index.html")
uri should haveParameter("q")
uri should haveFragment("results")
  • Date matchers - before / after / haveSameYear / haveSameDay / haveSameMonth / within

  • Collections - containNull, containDuplicates

  • Futures - completed, cancelled

  • String - haveLineCount, contain(regex)

  • Types - haveAnnotation(class)

  • Arrow matcher module

A new module has been added which includes matchers for Arrow - the popular and awesome functional programming library for Kotlin. To include this module add kotlintest-assertions-arrow to your build.

The included matchers are:

Option - Test that an Option has the given value or is a None. For example:

val option = Option.pure("foo")
option should beSome("foo")

val none = None
none should beNone()

Either- Test that an Either is either a Right or Left. For example:

Either.right("boo") should beRight("boo")
Either.left("boo") should beLeft("boo")

NonEmptyList- A collection (no pun intended) of matchers for Arrow's NonEmptyList. These mostly mirror the equivalent Collection matchers but for NELs. For example:

NonEmptyList.of(1, 2, null).shouldContainNull()
NonEmptyList.of(1, 2, 3, 4).shouldBeSorted<Int>()
NonEmptyList.of(1, 2, 3, 3).shouldHaveDuplicates()
NonEmptyList.of(1, 2, 3).shouldContain(2)
NonEmptyList.of(1, 2, 3).shouldHaveSize(3)
NonEmptyList.of(1, 2, 3).shouldContainNoNulls()
NonEmptyList.of(null, null, null).shouldContainOnlyNulls()
NonEmptyList.of(1, 2, 3, 4, 5).shouldContainAll(3, 2, 1)

Try - Test that a Try is either Success or Failure.

Try.Success("foo") should beSuccess("foo")
Try.Failure<Nothing>(RuntimeException()) should beFailure()

Validation - Asserts that a Validation is either Valid or an Invalid

Valid("foo") should beValid()
Invalid(RuntimeException()) should beInvalid()
  • Generator Bind

A powerful way of generating random class instances from primitive generators is to use the new bind function. A simple example is to take a data class of two fields, and then use two base generators and bind them to create random values of that class.

data class User(val email: String, val id: Int)

val userGen = Gen.bind(Gen.string(), Gen.positiveIntegers(), ::User)

assertAll(userGen) { shouldNotBe null should beGreaterThan(0)
  • Property Testing: Classify

When using property testing, it can be useful to see the distribution of values generated, to ensure you're getting a good spread of values and not just trival ones. For example, you might want to run a test on a String and you want to ensure you're getting good amounts of strings with whitespace.

To generate stats on the distribution, use classify with a predicate, a label if the predicate passes, and a label if the predicate fails. For example:

assertAll(Gen.string()) { a ->
classify(a.contains(" "), "has whitespace", "no whitespace")
// some test

And this will output something like:

63.70% no whitespace
36.30% has whitespace

So we can see we're getting a good spread of both types of value.

You don't have to include two labels if you just wish to tag the "true" case, and you can include more than one classification. For example:

forAll( { a ->
classify(a == 0, "zero")
classify(a % 2 == 0, "even number", "odd number")
a + a == 2 * a

This will output something like:

51.60% even number
48.40% odd number
0.10% zero
  • Property Testing: Shrinking

  • Tag Extensions

A new type of extension has been added called TagExtension. Implementations can override the tags() function defined in this interface to dynamically return the Tag instances that should be active at any moment. The existing system properties kotlintest.tags.include and kotlintest.tags.exclude are still valid and are not deprecated, but adding this new extension means extended scope for more complicated logic at runtime.

An example might be to disable any Hadoop tests when not running in an environment that doesn't have the hadoop home env variable set. After creating a TagExtension it must be registered with the project config.

object Hadoop : Tag()

object HadoopTagExtension : TagExtension {
override fun tags(): Tags =
if (System.getenv().containsKey("HADOOP_HOME")) Tags.include(Hadoop) else Tags.exclude(Hadoop)

object MyProjectConfig : AbstractProjectConfig() {
override fun extensions(): List<Extension> = listOf(HadoopTagExtension)

object SimpleTest : StringSpec({
"simple test" {
// this test would only run on environments that have hadoop configured
}.config(tags = setOf(Hadoop))
  • Discovery Extensions: instantiate()

Inside the DiscoveryExtension interface the function fun <T : Spec> instantiate(clazz: KClass<T\>): Spec? has been added which allows you to extend the way new instances of Spec are created. By default, a no-args constructor is assumed. However, if this function is overridden then it's possible to support Spec classes which have other constructors. For example, the Spring module now supports constructor injection using this extension. Other use cases might be when you want to always inject some config class, or if you want to ensure that all your tests extend some custom interface or superclass.

As a reminder, DiscoveryExtension instances are added to Project config.

  • System out / error extensions

An extension that allows you to test for a function that writes to System.out or System.err. To use this extension add the module kotlintest-extensions-system to your build.

By adding the NoSystemOutListener or NoSystemErrListener to your config or spec classes, anytime a function tries to write to either of these streams, a SystemOutWriteException or SystemErrWriteException will be raised with the string that the function tried to write. This allows you to test for the exception in your code.

For example:

class NoSystemOutOrErrTest : StringSpec() {

override fun listeners() = listOf(NoSystemOutListener, NoSystemErrListener)

init {

"System.out should throw an exception when the listener is added" {
shouldThrow<SystemOutWriteException> {
}.str shouldBe "boom"

"System.err should throw an exception when the listener is added" {
shouldThrow<SystemErrWriteException> {
}.str shouldBe "boom"
  • System.exit extension

Another extension that is part of the kotlintest-extensions-system module. This extension will allow you to test if System.exit(Int) is invoked in a function. It achieves this by intercepting any calls to System.exit and instead of terminating the JVM, it will throw a SystemExitException with the exit code.

For example:

class SystemExitTest : StringSpec() {

override fun listeners() = listOf(SpecSystemExitListener)

init {

"System.exit should throw an exception when the listener is added" {
shouldThrow<SystemExitException> {
}.exitCode shouldBe 123
  • Spring Module Updates

The spring extension module kotlintest-extensions-spring has been updated to allow for constructor injection. This new extension is called SpringAutowireConstructorExtension and must be added to your `ProjectConfig. Then you can use injected dependencies directly in the primary constructor of your test class.

For example:

@ContextConfiguration(classes = [(Components::class)])
class SpringAutowiredConstructorTest(service: UserService) : WordSpec({
"SpringListener" should {
"have autowired the service" {
service.repository.findUser().name shouldBe "system_user"
  • JUnit 4 Runner

A JUnit 4 runner has been added which allows KotlinTest to run using the legacy JUnit 4 platform. To use this, add kotlintest-runner-junit4 to your build instead of kotlintest-runner-junit5.

Note: This is intended for use when junit5 cannot be used. It should not be the first choice as functionality is restricted.


  • In intellij, test output will not be nested
  • Project wide beforeAll/afterAll cannot be supported.

Version 3.0.x - March 29 2018

  • Module split out

KotlinTest has been split into multiple modules. These include core, assertions, the junit runner, and extensions such as spring, allure and junit-xml.

The idea is that in a future release, further runners could be added (TestNG) or for JS support (once multi-platform Kotlin is out of beta). When upgrading you will typically want to add the kotlintest-core, kotlintest-assertions and kotlintest-runner-junit5 to your build rather than the old kotlintest module which is now defunct. When upgrading, you might find that you need to update imports to some matchers.

testCompile 'io.kotlintest:kotlintest-core:3.0.0'
testCompile 'io.kotlintest:kotlintest-assertions:3.0.0'
testCompile 'io.kotlintest:kotlintest-runner-junit5:3.0.0'

Gradle Users:

Also you must include apply plugin: 'org.junit.platform.gradle.plugin' in your project and classpath "org.junit.platform:junit-platform-gradle-plugin:1.1.0" to the dependencies section of your buildscript or tests will not run (or worse, will hang). This allows gradle to execute jUnit-platform-5 based tests (which KotlinTest builds upon). Note: Gradle says that this is not required as of 4.6 but even with 4.6 it seems to be required.

Maven users:

You need to include the following in your plugins:


And you must include


as a regular dependency.

  • Breaking: ProjectConfig

Project wide config in KotlinTest is controlled by implementing a subclass of AbstractProjectConfig. In previous versions you could call this what you wanted, and place it where you wanted, and KotlinTest would attempt to find it and use it. This was the cause of many bug reports about project start up times and reflection errors. So in version 3.0.x onwards, KotlinTest will no longer attempt to scan the classpath.

Instead you must call this class ProjectConfig and place it in a package io.kotlintest.provided. It must still be a subclass of AbstractProjectConfig This means kotlintest can do a simple Class.forName to find it, and so there is no startup penalty nor reflection issues.

Project config now allows you to register multiple types of extensions and listeners, as well as setting parallelism.

  • Breaking: Interceptors have been deprecated and replaced with Listeners

The previous inteceptors were sometimes confusing. You had to invoke the continuation function or the spec/test would not execute. Not invoking the function didn't mean the spec/test was skipped, but that it would hang.

So interceptors are deprecated, and in some places removed. Those are not removed are now located in classes called SpecExtension and TestCaseExtension and those interfaces should be used rather than functions directly.

Here is an example of a migrated interceptor.

val mySpecExtension = object : SpecExtension {
override fun intercept(spec: Spec, process: () -> Unit) {
println("Before spec!")
println("After spec!")

As a replacement, in 3.0.0 we've added the TestListener interface which is the more traditional before/after style callbacks. In addition, these methods include the result of the test (success, fail, error, skipped) which gives you more context in writing plugins. The TestListener interface offers everything the old interceptors could do, and more.

Here is an example of a simple listener.

object TimeTracker : TestListener {

var started = 0L

override fun beforeTest(description: Description) {
TimeTrackerTest.started = System.currentTimeMillis()

override fun afterTest(description: Description, result: TestResult) {
val duration = System.currentTimeMillis() - TimeTrackerTest.started
println("Test ${description.fullName()} took ${duration}ms")

If you want to use these methods in a Spec itself, then you can just override the functions directly because a Spec is already a TestListener.

object TimeTracker : WordSpec() {

var started = 0L

override fun beforeTest(description: Description) {
started = System.currentTimeMillis()

override fun afterTest(description: Description, result: TestResult) {
val duration = System.currentTimeMillis() - started
println("Test ${description.fullName()} took ${duration}ms")

init {
"some test" should {
"be timed" {
// test here

Listeners can be added project wide by overriding listeners() in the ProjectConfig.

Note: In the next release, new Extension functions will be added which will be similar to the old interceptors, but with complete control over the lifecycle. For instance, a future intercept method will enforce that the user skip, run or abort a test in the around advice. They will be more complex, and so suited to more advanced use cases. The new TestListener interface will remain of course, and is the preferred option.

  • Parallelism

If you want to run more than one spec class in parallel, you can by overriding parallelism inside your projects ProjectConfig or by supplying the system property kotlintest.parallelism.

Note the system property always takes precedence over the config.

  • Futures Support

Test cases now support waiting on futures in a neat way. If you have a value in a CompletableFuture that you want to test against once it completes, then you can do this like this:

val stringFuture: CompletableFuture<String> = ...

"My future test" should {
"support CompletableFuture<T\>" {
whenReady(stringFuture) {
it shouldBe "wibble"
  • Breaking: Exception Matcher Changes

The shouldThrow<T\> method has been changed to also test for subclasses. For example, shouldThrow<IOException> will also match exceptions of type FileNotFoundException. This is different to the behavior in all previous KotlinTest versions. If you wish to have functionality as before - testing exactly for that type - then you can use the newly added shouldThrowExactly<T\>.

  • JUnit XML Module

Support for writing out reports in junit-format XML has added via the kotlintest-extensions-junitxml module which you will need to add to your build. This module provides a JUnitXmlListener which you can register with your project to autowire your tests. You can register this by overriding listeners() in ProjectConfig.

class ProjectConfig : AbstractProjectConfig() {
override fun listeners() = listOf(JUnitXmlListener)
  • Spring Module

Spring support has been added via the kotlintest-extensions-spring module which you will need to add to your build. This module provides a SpringListener which you can register with your project to autowire your tests. You can register this for just some classes by overriding the listeners() function inside your spec, for example:

class MySpec : ParentSpec() {
override fun listeners() = listOf(SpringListener)

Or you can register this for all classes by adding it to the ProjectConfig. See the section on ProjectConfig for how to do this.

  • Breaking: Tag System Property Rename

The system property used to include/exclude tags has been renamed to kotlintest.tags.include and kotlintest.tags.exclude. Make sure you update your build jobs to set the right properties as the old ones no longer have any effect. If the old tags are detected then a warning message will be emitted on startup.

  • New Matchers

beInstanceOf<T\> has been added to easily test that a class is an instance of T. This is in addition to the more verbose beInstanceOf(SomeType::class).

The following matchers have been added for maps: containAll, haveKeys, haveValues. These will output helpful error messages showing you which keys/values or entries were missing.

New matchers added for Strings: haveSameLengthAs(other), beEmpty(), beBlank(), containOnlyDigits(), containADigit(), containIgnoringCase(substring), lowerCase(), upperCase().

New matchers for URIs: haveHost(hostname), havePort(port), haveScheme(scheme).

New matchers for collections: containNoNulls(), containOnlyNulls()

  • Breaking: One instance per test changes

One instance per test is no longer supported for specs which offer nested scopes. For example, WordSpec. This is because of the tricky nature of having nested closures work across fresh instances of the spec. When using one instance per test, a fresh spec class is required for each test, but that means selectively executing some closures and not others in order to ensure the correct state. This has proved the largest source of bugs in previous versions.

KotlinTest 3.0.x takes a simplified approach. If you want the flexibilty to lay out your tests with nested scopes, then all tests will execute in the same instance (like Spek and ScalaTest). If you want each test to have it's own instance (like jUnit) then you can either split up your tests into multiple files, or use a "flat" spec like FunSpec or StringSpec.

This keeps the implementation an order of magnitude simplier (and therefore less likely to lead to bugs) while offering a pragmatic approach to keeping both sets of fans happy.

  • New Specs

Multiple new specs have been added. These are: AnnotationSpec, DescribeSpec and ExpectSpec. Expect spec allows you to use the context and expect keywords in your tests, like so:

class ExpectSpecExample : ExpectSpec() {
init {
context("some context") {
expect("some test") {
// test here
context("nested context even") {
expect("some test") {
// test here

The AnnotationSpec offers functionality to mimic jUnit, in that tests are simply functions annotated with @io.kotlintest.specs.Test. For example:

class AnnotationSpecExample : AnnotationSpec() {

fun test1() {


fun test2() {


And finally, the DescribeSpec is similar to SpekFramework, using describe, and, and it. This makes it very useful for those people who are looking to migrate to KotlinTest from SpekFramework.

class DescribeSpecExample : DescribeSpec() {
init {
describe("some context") {
it("test name") {
// test here
describe("nested contexts") {
and("another context") {
it("test name") {
// test here
  • Property Testing with Matchers

The ability to use matchers in property testing has been added. Previously property testing worked only with functions that returned a Boolean, like:

"startsWith" {
forAll(Gen.string(), Gen.string(), { a, b ->
(a + b).startsWith(a)

But now you can use assertAll and assertNone and then use regular matchers inside the block. For example:

"startsWith" {
assertAll(Gen.string(), Gen.string(), { a, b ->
a + b should startWith(a)

This gives you the ability to use multiple matchers inside the same block, and not have to worry about combining all possible errors into a single boolean result.

  • Generator Edge Cases

Staying with property testing - the Generator interface has been changed to now provide two types of data.

The first are values that should always be included - those edge cases values which are common sources of bugs. For example, a generator for Ints should always include values like zero, minus 1, positive 1, Integer.MAXVALUE and Integer.MIN_VALUE. Another example would be for a generator for enums. That should include _all the values of the enum to ensure each value is tested.

The second set of values are random values, which are used to give us a greater breadth of values tested. The Int generator should return random ints from across the entire integer range.

Previously generators used by property testing would only include random values, which meant you were very unlikely to see the edge cases that usually cause issues - like the aforementioned Integer MAX / MIN. Now you are guaranteed to get the edge cases first and the random values afterwards.

  • Breaking: MockitoSugar removed

This interface added a couple of helpers for Mockito, and was used primarily before Kotlin specific mocking libraries appeared. Now there is little value in this mini-wrapper so it was removed. Simply add whatever mocking library you like to your build and use it as normal.

  • CsvDataSource

This class has been added for loading data for table testing. A simple example:

class CsvDataSourceTest : WordSpec() {
init {

"CsvDataSource" should {
"read data from csv file" {

val source = CsvDataSource(javaClass.getResourceAsStream("/user_data.csv"), CsvFormat())

val table = source.createTable<Long, String, String>(
{ it: Record -> Row3(it.getLong("id"), it.getString("name"), it.getString("location")) },
{ it: Array<String> -> Headers3(it[0], it[1], it[2]) }

forAll(table) { a, b, c ->
a shouldBe gt(0)
b shouldNotBe null
c shouldNotBe null
  • Matcher Negation Errors

All matchers now have the ability to report a better error when used with shouldNot and shouldNotBe. Previously a generic error was generated - which was usually the normal error but with a prefix like "NOT:" but now each built in matcher will provide a full message, for example: Collection should not contain element 'foo'

Version 2.0.0, released 2017-03-26

Closed Issues


  • You can write tests alternatively into a lambda parameter in the class constructor, eg:
class StringSpecExample : StringSpec({
"strings.size should return size of string" {
"hello".length shouldBe 5
"hello" should haveLength(5)
  • Added forNone for table tests, eg
val table = table(
headers("a", "b"),
row(0L, 2L),
row(2L, 2L),
row(4L, 5L),
row(4L, 6L)

forNone(table) { a, b ->
3 shouldBe between(a, b)
  • Interceptors have been added. Interceptors allow code to be executed before and after a test. See the main readme for more info.

  • Simplified ability to add custom matchers. Simple implement Matcher<T\> interface. See readme for more information.

  • Added shouldNot to invert matchers. Eg, "hello" shouldNot include("hallo")

  • Deprecated matchers which do not implement Matcher<T>. Eg, should have substring(x) has been deprecated in favour of "hello" should include("l"). This is because instances of Matcher<T> can be combined with or and and and can be negated with shouldNot.

  • Added between matcher for int and long, eg

3 shouldBe between(2, 5)

  • Added singleElement matcher for collections, eg

x shouldBe singleElement(y)

  • Added sorted matcher for collections, eg

listOf(1,2,3) shouldBe sorted<Int>()

  • Now supports comparsion of arrays #116

  • Added Gen.oneOf

    to create a generator that returns one of the values for the given Enum class.


  • Tags are objects derived from Tag class now.
  • Tags can now be included and/or exluded. It is no longer the case that all untagged tests are always executed.
  • Fixed bugs with parenthesis breaking layout in Intellij #112


  • FlatSpec was removed because it has an irregular syntax with config and is essentially the same as StringSpec, but more complicated.
  • Deprecated method overloads with duration: Long, unit: TimeUnit
  • expecting for testing exceptions (use shouldThrow now)

Version 1.3.2, released 2016-07-05


  • Added a shouldBe exactly(b) matcher for doubles

  • kotlintest only pulls in mockito-core now instead of mockito-all

Version 1.3.1, released 2016-07-03


  • Bumped Kotlin version to 1.0.3

Version 1.3.0, released 2016-07-03

Closed Issues


  • StringSpec. You can use simply use Strings as the basis for tests, eg:
class StringSpecExample : StringSpec() {
init {
"strings.size should return size of string" {
"hello".length shouldBe 5
"hello" should haveLength(5)

"strings should support config" {
"hello".length shouldBe 5
}.config(invocations = 5)
  • Table Tests. Tables allow you to manually specific combinations of values that should be used, and are useful for edge cases and other specific values you want to test. The headers are used for when values fail, the output can show you what inputs were used for what labels. An example of using a table consisting of two-value tuples:
class TableExample : StringSpec(), TableTesting {
init {
"numbers should be prime" {
val table = table(
headers("a", "b"),
row(5, 5),
row(4, 6),
row(3, 7)
forAll(table) { a, b ->
a + b == 10
  • Property tests. Property tests automatically generate values for testings. You provide, or have KotlinTest provide for you, generators, which will generate a set of values and the unit test will be executed for each of those values. An example using two strings and asserting that the lengths are correct:
class PropertyExample: StringSpec() {

"String size" {
forAll({ a: String, b: String ->
(a + b).length == a.length + b.length


That test will be executed 100 times with random values in each test. See more in the readme.

  • autoClose. Fields of type Closeable can be registered for automatic resource closing:
class StringSpecExample : StringSpec() {
val reader = autoClose(StringReader("xyz"))

  • haveLength matcher. You can now write for strings:
someString should haveLength(10)
  • haveSize matcher. You can now write for collections:
myCollection should haveSize(4)
  • contain matcher. You can now write
val col = listOf(1,2,3,4,5)
col should contain(4)
  • containInAnyOrder matcher. You can now write
val col = listOf(1,2,3,4,5)
col should containInAnyOrder(4,2,3)
  • haveKey Map<K,V> matcher. You can now write
val map = mapOf(Pair(1, "a"), Pair(2, "b"))
map should haveKey(1)
  • haveValue Map<K,V> matcher. You can now write
val map = mapOf(Pair(1, "a"), Pair(2, "b"))
map should haveValue("a")
  • contain Map<K,V> matcher. You can now write
val map = mapOf(Pair(1, "a"), Pair(2, "b"))
map should contain(1, "a")
  • beTheSameInstanceAs reference matcher. This is an alias for x should be theSameInstanceAs(y), allowing x should beTheSameInstanceAs(y) which fits in with new matcher style.


Replaced timeout + timeUnit with Duration (#29)

You can now write config(timeout = 2.seconds) instead of config(timeout = 2, timeoutUnit = TimeUnit.SECONDS).