MockK

Additional

Language
Kotlin
Version
1.9.3.kotlin12 (Mar 25, 2019)
Created
Oct 18, 2017
Updated
Nov 29, 2019
Owner
Oleksiy Pylypenko (oleksiyp)
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Tobias Preuss (johnjohndoe)
jameskbride
Nishant Srivastava (nisrulz)
Sascha Peilicke (saschpe)
mkobit
ikesyo
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yanzm
Kerooker
Oleksiy Pylypenko (oleksiyp)
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Blurb

Kotlin Academy articles

Check the series of articles "Mocking is not rocket science" at Kt. Academy describing MockK from the very basics of mocking up to description of all advanced features.

Spring support

Version twist

From version 1.9 MockK switched to Kotlin 1.3 and Coroutines 1.0 by default and other branch 1.9.kotlin12 may be used for compatibility with Kotlin 1.2.

Known issues & worth to remember

  • Some known issues related to Kotlin 1.3, Gradle 5 and Spring Boot were fixed in MockK 1.9. Please report if you face any problems.
  • PowerMock needs a workaround to run together with MockK #79. (not sure after workaround if it is generally usable or not, please somebody report it)

Table of contents:

  • auto-gen TOC: {:toc}

Examples & articles

Installation

All you need to get started is just to add a dependency to MockK library.

Gradle/maven dependency

ApproachInstruction
   
testImplementation "io.mockk:mockk:{version}"
(Kotlin DSL)    
testImplementation("io.mockk:mockk:{version}")
<dependency>
    <groupId>io.mockk</groupId>
    <artifactId>mockk</artifactId>
    <version>{version}</version>
    <scope>test</scope>
</dependency>
Unit    
testImplementation "io.mockk:mockk:{version}"
Instrumented    
androidTestImplementation "io.mockk:mockk-android:{version}"
Common multiplatform    
testImplementation "io.mockk:mockk-common:{version}"

where {version} corresponds to version as below:

  • Kotlin 1.3+ and Coroutines 1.0+ Version:
  • Kotlin 1.2 Compatible Version:

DSL examples

Simplest example. By default mocks are strict, so you need to provide some behaviour.

val car = mockk<Car>()

every { car.drive(Direction.NORTH) } returns Outcome.OK

car.drive(Direction.NORTH) // returns OK

verify { car.drive(Direction.NORTH) }

confirmVerified(car)

Annotations

You can use annotations to simplify the creation of mock objects:

class TrafficSystem {
  lateinit var car1: Car
  
  lateinit var car2: Car
  
  lateinit var car3: Car
}

class CarTest {
  @MockK
  lateinit var car1: Car

  @RelaxedMockK
  lateinit var car2: Car

  @MockK(relaxUnitFun = true)
  lateinit var car3: Car

  @SpyK
  var car4 = Car()
  
  @InjectMockKs
  var trafficSystem = TrafficSystem()
  
  @Before
  fun setUp() = MockKAnnotations.init(this, relaxUnitFun = true) // turn relaxUnitFun on for all mocks

  @Test
  fun calculateAddsValues1() {
      // ... use car1, car2, car3 and car4
  }
}

Injection first tries to match properties by name, then by class or superclass. Check the lookupType parameter for customization.

Properties are injected even if private is applied. Constructors for injection are selected from the biggest number of arguments to lowest.

@InjectMockKs by default is injecting only lateinit vars or vars that are not assigned. To change this, use overrideValues = true. This would assign the value even if it is already somehow initialized. To inject vals, use injectImmutable = true. For a shorter notation use @OverrideMockKs which does the same as @InjectMockKs by default, but turns these two flags on.

JUnit5

In JUnit5 you can use MockKExtension to initialize your mocks.

@ExtendWith(MockKExtension::class)
class CarTest {
  @MockK
  lateinit var car1: Car

  @RelaxedMockK
  lateinit var car2: Car

  @MockK(relaxUnitFun = true)
  lateinit var car3: Car

  @SpyK
  var car4 = Car()

  @Test
  fun calculateAddsValues1() {
      // ... use car1, car2, car3 and car4
  }
}

Additionally, it adds the possibility to use @MockK and @RelaxedMockK on test function parameters:

@Test
fun calculateAddsValues1(@MockK car1: Car, @RelaxedMockK car2: Car) {
  // ... use car1 and car2
}

Spy

Spies allow to mix mocks and real objects.

val car = spyk(Car()) // or spyk<Car>() to call default constructor

car.drive(Direction.NORTH) // returns whatever real function of Car returns

verify { car.drive(Direction.NORTH) }

confirmVerified(car)

Note: the spy object is a copy of a passed object.

Relaxed mock

A relaxed mock is the mock that returns some simple value for all functions. This allows to skip specifying behavior for each case, while still allowing to stub things you need. For reference types, chained mocks are returned.

val car = mockk<Car>(relaxed = true)

car.drive(Direction.NORTH) // returns null

verify { car.drive(Direction.NORTH) }

confirmVerified(car)

Note: relaxed mocking is working badly with generic return types. A class cast exception is usually thrown in this case. Opt for stubbing manually in case of a generic return type.

Workaround:

val func = mockk<() -> Car>(relaxed = true) // in this case invoke function has generic return type

// this line is workaround, without it the relaxed mock would throw a class cast exception on the next line
every { func() } returns Car() // or you can return mockk() for example 

func()

Mock relaxed for functions returning Unit

In case you would like Unit returning functions to be relaxed, you can use relaxUnitFun = true as an argument to the mockk function, @MockKannotation or MockKAnnotations.init function.

Function:

mockk<MockCls>(relaxUnitFun = true)

Annotation:

@MockK(relaxUnitFun = true)
lateinit var mock1: RurfMockCls
init {
    MockKAnnotations.init(this)
}

MockKAnnotations.init:

@MockK
lateinit var mock2: RurfMockCls
init {
    MockKAnnotations.init(this, relaxUnitFun = true)
}

Object mocks

Objects can be transformed to mocks in the following way:

object MockObj {
  fun add(a: Int, b: Int) = a + b
}

mockkObject(MockObj) // applies mocking to an Object

assertEquals(3, MockObj.add(1, 2))

every { MockObj.add(1, 2) } returns 55

assertEquals(55, MockObj.add(1, 2))

To revert back, use unmockkAll or unmockkObject:

@Before
fun beforeTests() {
    mockkObject(MockObj)
    every { MockObj.add(1,2) } returns 55
}

@Test
fun willUseMockBehaviour() {
    assertEquals(55, MockObj.add(1,2))
}

@After
fun afterTests() {
    unmockkAll()
    // or unmockkObject(MockObj)
}

Despite the Kotlin language limits, you can create new instances of objects if required by testing logic:

val newObjectMock = mockk<MockObj>()

Class mock

Sometimes you need a mock of arbitrary class. Use mockkClass in those cases.

val car = mockkClass(Car::class)

every { car.drive(Direction.NORTH) } returns Outcome.OK

car.drive(Direction.NORTH) // returns OK

verify { car.drive(Direction.NORTH) }

Enumeration mocks

Enums can be mocked using mockkObject:

enum class Enumeration(val goodInt: Int) {
    CONSTANT(35),
    OTHER_CONSTANT(45);
}

mockkObject(Enumeration.CONSTANT)
every { Enumeration.CONSTANT.goodInt } returns 42
assertEquals(42, Enumeration.CONSTANT.goodInt)

Constructor mocks

Sometimes, especially in code you don't own, you need to mock newly created objects. For this purpose, the following constructs are provided:

class MockCls {
  fun add(a: Int, b: Int) = a + b
}

mockkConstructor(MockCls::class)

every { anyConstructed<MockCls>().add(1, 2) } returns 4

assertEquals(4, MockCls().add(1, 2)) // note new object is created

verify { anyConstructed<MockCls>().add(1, 2) }

The basic idea is that just after the constructor of the mocked class is executed (any of them), objects become a constructed mock. Mocking behavior of such a mock is connected to the special prototype mock denoted by anyConstructed<MockCls>(). There is one instance per class of such a prototype mock. Call recording also happens to the prototype mock. If no behavior for the function is specified then the original function is executed.

Partial argument matching

You can mix both regular arguments and matchers:

val car = mockk<Car>()

every { 
  car.recordTelemetry(
    speed = more(50),
    direction = Direction.NORTH, // here eq() is used
    lat = any(),
    long = any()
  )
} returns Outcome.RECORDED

obj.recordTelemetry(60, Direction.NORTH, 51.1377382, 17.0257142)

verify { obj.recordTelemetry(60, Direction.NORTH, 51.1377382, 17.0257142) }

confirmVerified(obj)

Chained calls

You can stub chains of calls:

val car = mockk<Car>()

every { car.door(DoorType.FRONT_LEFT).windowState() } returns WindowState.UP

car.door(DoorType.FRONT_LEFT) // returns chained mock for Door
car.door(DoorType.FRONT_LEFT).windowState() // returns WindowState.UP

verify { car.door(DoorType.FRONT_LEFT).windowState() }

confirmVerified(car)

Note: in case the function's return type is generic then the information about the actual type is gone. To make chained calls work, additional information is required. Most of the time the framework will catch the cast exception and do autohinting. In the case it is explicitly required, use hint before making the next call.

every { obj.op2(1, 2).hint(Int::class).op1(3, 4) } returns 5

Hierarchical mocking

From version 1.9.1 mocks may be chained into hierarchies:

interface AddressBook {
    val contacts: List<Contact>
}

interface Contact {
    val name: String
    val telephone: String
    val address: Address
}

interface Address {
    val city: String
    val zip: String
}

val addressBook = mockk<AddressBook> {
    every { contacts } returns listOf(
        mockk {
            every { name } returns "John"
            every { telephone } returns "123-456-789"
            every { address.city } returns "New-York"
            every { address.zip } returns "123-45"
        },
        mockk {
            every { name } returns "Alex"
            every { telephone } returns "789-456-123"
            every { address } returns mockk {
                every { city } returns "Wroclaw"
                every { zip } returns "543-21"
            }
        }
    )
}

Capturing

You can capture an argument to a CapturingSlot or MutableList:

val car = mockk<Car>()

val slot = slot<Double>()
val list = mutableListOf<Double>()

every {
  obj.recordTelemetry(
    speed = capture(slot), // makes mock match call with any value for `speed` and record it in a slot
    direction = Direction.NORTH // makes mock and capturing only match calls with specific `direction`. Use `any()` to match calls with any `direction`
  )
} answers {
  println(slot.captured)

  Outcome.RECORDED
}


every {
  obj.recordTelemetry(
    speed = capture(list),
    direction = Direction.SOUTH
  )
} answers {
  println(list)

  Outcome.RECORDED
}

obj.recordTelemetry(speed = 15, direction = Direction.NORTH) // prints 15
obj.recordTelemetry(speed = 16, direction = Direction.SOUTH) // prints 16

verify(exactly = 2) { obj.recordTelemetry(speed = or(15, 16), direction = any()) }

confirmVerified(obj)

Verification atLeast, atMost or exactly times

You can check the call count with the atLeast, atMost or exactly parameters:

val car = mockk<Car>(relaxed = true)

car.accelerate(fromSpeed = 10, toSpeed = 20)
car.accelerate(fromSpeed = 10, toSpeed = 30)
car.accelerate(fromSpeed = 20, toSpeed = 30)

// all pass
verify(atLeast = 3) { car.accelerate(allAny()) }
verify(atMost  = 2) { car.accelerate(fromSpeed = 10, toSpeed = or(20, 30)) }
verify(exactly = 1) { car.accelerate(fromSpeed = 10, toSpeed = 20) }
verify(exactly = 0) { car.accelerate(fromSpeed = 30, toSpeed = 10) } // means no calls were performed

confirmVerified(car)

Verification order

  • verifyAll verifies that all calls happened without checking their order.
  • verifySequence verifies that the calls happened in a specified sequence.
  • verifyOrder verifies that calls happened in a specific order.
  • wasNot Called verifies that the mock or the list of mocks was not called at all.
class MockedClass {
    fun sum(a: Int, b: Int) = a + b
}

val obj = mockk<MockedClass>()
val slot = slot<Int>()

every {
    obj.sum(any(), capture(slot))
} answers {
    1 + firstArg<Int>() + slot.captured
}

obj.sum(1, 2) // returns 4
obj.sum(1, 3) // returns 5
obj.sum(2, 2) // returns 5

verifyAll {
    obj.sum(1, 3)
    obj.sum(1, 2)
    obj.sum(2, 2)
}

verifySequence {
    obj.sum(1, 2)
    obj.sum(1, 3)
    obj.sum(2, 2)
}

verifyOrder {
    obj.sum(1, 2)
    obj.sum(2, 2)
}

val obj2 = mockk<MockedClass>()
val obj3 = mockk<MockedClass>()
verify {
    listOf(obj2, obj3) wasNot Called
}

confirmVerified(obj)

Verification confirmation

To double check that all calls were verified by verify... constructs, you can use confirmVerified:

confirmVerified(mock1, mock2)

It does not make much sense to use it for verifySequence and verifyAll as these verification methods already exhaustively cover all calls with verification.

It will throw an exception in case there are some calls left without verification.

Some calls may be skipped from such confirmation, check the next section for more details.

val car = mockk<Car>()

every { car.drive(Direction.NORTH) } returns Outcome.OK
every { car.drive(Direction.SOUTH) } returns Outcome.OK

car.drive(Direction.NORTH) // returns OK
car.drive(Direction.SOUTH) // returns OK

verify {
    car.drive(Direction.SOUTH)
    car.drive(Direction.NORTH)
}

confirmVerified(car) // makes sure all calls were covered with verification

Recording exclusions

To exclude some not so important calls from being recorded you can use excludeRecords:

excludeRecords { mock.operation(any(), 5) }

All matching calls will be excluded from recording. This may be useful in case you are using exhaustive verification: verifyAll, verifySequence or confirmVerified.

val car = mockk<Car>()

every { car.drive(Direction.NORTH) } returns Outcome.OK
every { car.drive(Direction.SOUTH) } returns Outcome.OK

excludeRecords { car.drive(Direction.SOUTH) }

car.drive(Direction.NORTH) // returns OK
car.drive(Direction.SOUTH) // returns OK

verify {
    car.drive(Direction.NORTH)
}

confirmVerified(car) // car.drive(Direction.SOUTH) was excluded, so confirmation is fine with only car.drive(Direction.NORTH)

Verification timeout

To verify concurrent operations, you can use timeout = xxx:

mockk<MockCls> {
    every { sum(1, 2) } returns 4

    Thread {
        Thread.sleep(2000)
        sum(1, 2)
    }.start()

    verify(timeout = 3000) { sum(1, 2) }
}

This will wait until one of two following states: either verification is passed or timeout is reached.

Returning Unit

If the function is returning Unit you can use the just Runs construct:

class MockedClass {
    fun sum(a: Int, b: Int): Unit {
        println(a + b)
    }
}

val obj = mockk<MockedClass>()

every { obj.sum(any(), 3) } just Runs

obj.sum(1, 1)
obj.sum(1, 2)
obj.sum(1, 3)

verify {
    obj.sum(1, 1)
    obj.sum(1, 2)
    obj.sum(1, 3)
}

Coroutines

To mock coroutines you need to add another dependency to the support library.

Gradle
testCompile "org.jetbrains.kotlinx:kotlinx-coroutines-core:x.x"
Maven
<dependency>
    <groupId>org.jetbrains.kotlinx</groupId>
    <artifactId>kotlinx-coroutines-core</artifactId>
    <version>x.x</version>
    <scope>test</scope>
</dependency>

Then you can use coEvery, coVerify, coMatch, coAssert, coRun, coAnswers or coInvoke to mock suspend functions.

val car = mockk<Car>()

coEvery { car.drive(Direction.NORTH) } returns Outcome.OK

car.drive(Direction.NORTH) // returns OK

coVerify { car.drive(Direction.NORTH) }

Extension functions

There are three cases of extension function:

  • class wide
  • object wide
  • module wide

In case of an object or a class, you can mock extension functions just by creating a regular mockk:

data class Obj(val value: Int)

class Ext {
    fun Obj.extensionFunc() = value + 5
}

with(mockk<Ext>()) {
    every {
        Obj(5).extensionFunc()
    } returns 11

    assertEquals(11, Obj(5).extensionFunc())

    verify {
        Obj(5).extensionFunc()
    }
}

To mock module wide extension functions you need to build mockkStatic(...) with as argument the module's class name. For example "pkg.FileKt" for module File.kt in the pkg package.

data class Obj(val value: Int)

// declared in File.kt ("pkg" package)
fun Obj.extensionFunc() = value + 5

mockkStatic("pkg.FileKt")

every {
    Obj(5).extensionFunc()
} returns 11

assertEquals(11, Obj(5).extensionFunc())

verify {
    Obj(5).extensionFunc()
}

If @JvmName is used, specify it as a class name.

KHttp.kt:

@file:JvmName("KHttp")

package khttp
// ... KHttp code 

Testing code:

mockkStatic("khttp.KHttp")

Sometimes you need to know a little bit more to mock an extension function. For example File.endsWith() extension function has a totally unpredictable classname:

   mockkStatic("kotlin.io.FilesKt__UtilsKt")
   every { File("abc").endsWith(any<String>()) } returns true
   println(File("abc").endsWith("abc"))

This is standard Kotlin behaviour that may be unpredictable. Use Tools -> Kotlin -> Show Kotlin Bytecode or check .class files in JAR archive to detect such names.

Varargs

From version 1.9.1 more extended vararg handling is possible:

    interface ClsWithManyMany {
        fun manyMany(vararg x: Any): Int
    }

    val obj = mockk<ClsWithManyMany>()

    every { obj.manyMany(5, 6, *varargAll { it == 7 }) } returns 3

    println(obj.manyMany(5, 6, 7)) // 3
    println(obj.manyMany(5, 6, 7, 7)) // 3
    println(obj.manyMany(5, 6, 7, 7, 7)) // 3

    every { obj.manyMany(5, 6, *anyVararg(), 7) } returns 4

    println(obj.manyMany(5, 6, 1, 7)) // 4
    println(obj.manyMany(5, 6, 2, 3, 7)) // 4
    println(obj.manyMany(5, 6, 4, 5, 6, 7)) // 4

    every { obj.manyMany(5, 6, *varargAny { nArgs > 5 }, 7) } returns 5

    println(obj.manyMany(5, 6, 4, 5, 6, 7)) // 5
    println(obj.manyMany(5, 6, 4, 5, 6, 7, 7)) // 5

    every {
        obj.manyMany(5, 6, *varargAny {
            if (position < 3) it == 3 else it == 4
        }, 7)
    } returns 6
    
    println(obj.manyMany(5, 6, 3, 4, 7)) // 6
    println(obj.manyMany(5, 6, 3, 4, 4, 7)) // 6

Private functions mocking / dynamic calls

In case you have a need to mock private functions, you can do it via a dynamic call.

class Car {
    fun drive() = accelerate()

    private fun accelerate() = "going faster"
}

val mock = spyk<Car>(recordPrivateCalls = true)

every { mock["accelerate"]() } returns "going not so fast"

assertEquals("going not so fast", mock.drive())

verifySequence {
    mock.drive()
    mock["accelerate"]()
}

In case you want private calls to be verified, you should create a spyk with recordPrivateCalls = true

Additionally, a more verbose syntax allows you to get and set properties, combined with the same dynamic calls:

val mock = spyk(Team(), recordPrivateCalls = true)

every { mock getProperty "speed" } returns 33
every { mock setProperty "acceleration" value less(5) } just runs
every { mock invokeReturnsUnit "privateMethod" } just runs
every { mock invoke "openDoor" withArguments listOf("left", "rear") } returns "OK"

verify { mock getProperty "speed" }
verify { mock setProperty "acceleration" value less(5) }
verify { mock invoke "openDoor" withArguments listOf("left", "rear") }

Property backing fields

You can access the backing fields via fieldValue and use value for value being set.

Note: in the examples below, we use propertyType to specify the type of the fieldValue. This is needed because it is possible to capture the type automatically for the getter. Use nullablePropertyType to specify a nullable type.

val mock = spyk(MockCls(), recordPrivateCalls = true)

every { mock.property } answers { fieldValue + 6 }
every { mock.property = any() } propertyType Int::class answers { fieldValue += value }
every { mock getProperty "property" } propertyType Int::class answers { fieldValue + 6 }
every { mock setProperty "property" value any<Int>() } propertyType Int::class answers  { fieldValue += value }
every {
    mock.property = any()
} propertyType Int::class answers {
    fieldValue = value + 1
} andThen {
    fieldValue = value - 1
}

Multiple interfaces

Adding additional behaviours via interfaces and stubbing them:

val spy = spyk(System.out, moreInterfaces = Runnable::class)

spy.println(555)

every {
    (spy as Runnable).run()
} answers {
    (self as PrintStream).println("Run! Run! Run!")
}

val thread = Thread(spy as Runnable)
thread.start()
thread.join()

Mocking Nothing

Nothing special here. If you have a function returning Nothing:

fun quit(status: Int): Nothing {
    exitProcess(status)
}

Then you can for example throw an exception as behaviour:

every { quit(1) } throws Exception("this is a test")

Clearing vs Unmocking

  • clear - deletes internal state of objects associated with mock resulting in empty object
  • unmock - re-assigns transformation of classes back to original state prior to mock

Matcher extensibility

A very simple way is to create new matchers by attaching a function to MockKMatcherScope or MockKVerificationScope and using the match function:

    fun MockKMatcherScope.seqEq(seq: Sequence<String>) = match<Sequence<String>> {
        it.toList() == seq.toList()
    }

Also, it is possible to create more advanced matchers by implementing the Matcher interface.

Settings file

To adjust parameters globally, there is a possibility to specify a few settings in a resource file.

How to use:

  1. Create a io/mockk/settings.properties file in the resources.
  2. Put one of following options:
relaxed=true|false
relaxUnitFun=true|false
recordPrivateCalls=true|false

DSL tables

Here are a few tables to help you master the DSL.

Top level functions

Function Description
mockk<T>(...) builds a regular mock
spyk<T>() builds a spy using the default constructor
spyk(obj) builds a spy by copying from obj
slot creates a capturing slot
every starts a stubbing block
coEvery starts a stubbing block for coroutines
verify starts a verification block
coVerify starts a verification block for coroutines
verifyAll starts a verification block that should include all calls
coVerifyAll starts a verification block that should include all calls for coroutines
verifyOrder starts a verification block that checks the order
coVerifyOrder starts a verification block that checks the order for coroutines
verifySequence starts a verification block that checks whether all calls were made in a specified sequence
coVerifySequence starts a verification block that checks whether all calls were made in a specified sequence for coroutines
excludeRecords exclude some calls from being recorded
confirmVerified confirms that all recorded calls were verified
clearMocks clears specified mocks
registerInstanceFactory allows you to redefine the way of instantiation for certain object
mockkClass builds a regular mock by passing the class as parameter
mockkObject makes an object an object mock or clears it if was already transformed
unmockkObject makes an object mock back to a regular object
mockkStatic makes a static mock out of a class or clears it if it was already transformed
unmockkStatic makes a static mock back to a regular class
clearStaticMockk clears a static mock
mockkConstructor makes a constructor mock out of a class or clears it if it was already transformed
unmockkConstructor makes a constructor mock back to a regular class
clearConstructorMockk clears the constructor mock
unmockkAll unmocks object, static and constructor mocks
clearAllMocks clears regular, object, static and constructor mocks

Matchers

By default, simple arguments are matched using eq()

Matcher Description
any() matches any argument
allAny() special matcher that uses any() instead of eq() for matchers that are provided as simple arguments
isNull() checks if the value is null
isNull(inverse=true) checks if the value is not null
ofType(type) checks if the value belongs to the type
match { it.startsWith("string") } matches via the passed predicate
coMatch { it.startsWith("string") } matches via the passed coroutine predicate
matchNullable { it?.startsWith("string") } matches nullable value via the passed predicate
coMatchNullable { it?.startsWith("string") } matches nullable value via the passed coroutine predicate
eq(value) matches if the value is equal to the provided value via the deepEquals function
eq(value, inverse=true) matches if the value is not equal to the provided value via the deepEquals function
neq(value) matches if the value is not equal to the provided value via deepEquals function
refEq(value) matches if the value is equal to the provided value via reference comparison
refEq(value, inverse=true) matches if the value is not equal to the provided value via reference comparison
nrefEq(value) matches if the value is not equal to the provided value via reference comparison
cmpEq(value) matches if the value is equal to the provided value via the compareTo function
less(value) matches if the value is less than the provided value via the compareTo function
more(value) matches if the value is more than the provided value via the compareTo function
less(value, andEquals=true) matches if the value is less than or equal to the provided value via the compareTo function
more(value, andEquals=true) matches if the value is more than or equal to the provided value via the compareTo function
range(from, to, fromInclusive=true, toInclusive=true) matches if the value is in range via the compareTo function
and(left, right) combines two matchers via a logical and
or(left, right) combines two matchers via a logical or
not(matcher) negates the matcher
capture(slot) captures a value to a CapturingSlot
capture(mutableList) captures a value to a list
captureNullable(mutableList) captures a value to a list together with null values
captureLambda() captures a lambda
captureCoroutine() captures a coroutine
invoke(...) calls a matched argument
coInvoke(...) calls a matched argument for a coroutine
hint(cls) hints the next return type in case it's gotten erased
anyVararg() matches any elements in a vararg
varargAny(matcher) matches if any element is matching the matcher
varargAll(matcher) matches if all elements are matching the matcher
any...Vararg() matches any elements in vararg (specific to primitive type)
varargAny...(matcher) matches if any element is matching the matcher (specific to the primitive type)
varargAll...(matcher) matches if all elements are matching the matcher (specific to the primitive type)

A few special matchers available in verification mode only:

Matcher Description
withArg { code } matches any value and allows to execute some code
withNullableArg { code } matches any nullable value and allows to execute some code
coWithArg { code } matches any value and allows to execute some coroutine code
coWithNullableArg { code } matches any nullable value and allows to execute some coroutine code

Validators

Validator Description
verify { mock.call() } Do unordered verification that a call was performed
verify(inverse=true) { mock.call() } Do unordered verification that a call was not performed
verify(atLeast=n) { mock.call() } Do unordered verification that a call was performed at least n times
verify(atMost=n) { mock.call() } Do unordered verification that a call was performed at most n times
verify(exactly=n) { mock.call() } Do unordered verification that a call was performed exactly n times
verifyAll { mock.call1(); mock.call2() } Do unordered verification that only the specified calls were executed for the mentioned mocks
verifyOrder { mock.call1(); mock.call2() } Do verification that the sequence of calls went one after another
verifySequence { mock.call1(); mock.call2() } Do verification that only the specified sequence of calls were executed for the mentioned mocks
verify { mock wasNot Called } Do verification that a mock was not called
verify { listOf(mock1, mock2) wasNot Called } Do verification that a list of mocks were not called

Answers

An Answer can be followed up by one or more additional answers.

Answer Description
returns value specify that the matched call returns a specified value
returnsMany list specify that the matched call returns a value from the list, with subsequent calls returning the next element
throws ex specify that the matched call throws an exception
answers { code } specify that the matched call answers with a code block scoped with answer scope
coAnswers { code } specify that the matched call answers with a coroutine code block with answer scope
answers answerObj specify that the matched call answers with an Answer object
answers { nothing } specify that the matched call answers null
just Runs specify that the matched call is returning Unit (returns null)
propertyType Class specify the type of backing field accessor
nullablePropertyType Class specify the type of backing field accessor as a nullable type

Additional answer(s)

A next answer is returned on each consequent call and the last value is persisted. So this is similar to the returnsMany semantics.

Additional answer Description
andThen value specify that the matched call returns one specified value
andThenMany list specify that the matched call returns value from the list, returning each time next element
andThenThrows ex specify that the matched call throws an exception
andThen { code } specify that the matched call answers with a code block scoped with answer scope
coAndThen { code } specify that the matched call answers with a coroutine code block with answer scope
andThenAnswer answerObj specify that the matched call answers with an Answer object
andThen { nothing } specify that the matched call answers null

Answer scope

Parameter Description
call a call object that consists of an invocation and a matcher
invocation contains information regarding the actual function invoked
matcher contains information regarding the matcher used to match the invocation
self reference to the object invocation made
method reference to the function invocation made
args reference to the arguments of invocation
nArgs number of invocation argument
arg(n) n-th argument
firstArg() first argument
secondArg() second argument
thirdArg() third argument
lastArg() last argument
captured() the last element in the list for convenience when capturing to a list
lambda<...>().invoke() call the captured lambda
coroutine<...>().coInvoke() call the captured coroutine
nothing null value for returning nothing as an answer
fieldValue accessor to the property backing field
fieldValueAny accessor to the property backing field with Any? type
value value being set casted to same type as the property backing field
valueAny value being set with Any? type

Vararg scope

Parameter Description
position the position of an argument in vararg array
nArgs overall count of arguments in vararg array

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Contributors

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Getting Help

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To report bugs, please use the GitHub project.