The mockk from robertkeazor

Table of contents:

auto-gen TOC: {:toc}

Nice features

mocking final classes and functions (via inlining)
pure Kotlin mocking DSL
matchers partial specification
chained calls
matcher expressions
mocking coroutines
capturing lambdas
extension function mocking

Examples & articles

kotlin-fullstack-sample project covered with tests
DZone article
Habrahabr article (RU)

Installation

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

Gradle/maven dependency

Tool	Instruction
	testCompile "io.mockk:mockk:1.6"
	<dependency> <groupId>io.mockk</groupId> <artifactId>mockk</artifactId> <version>1.6</version> <scope>test</scope> </dependency>

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) }

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) }

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

Relaxed mock

Relaxed mock is the mock that returns some simple value for all functions. This allows to skip specifying behavior for each case, while still allow 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) }

Note: relaxed mocking is working badly with generic return type. Usually in this case class cast exception is thrown. You need to specify stubbing manually for case of 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 relaxed mock would throw class cast exception on the next line
every { func() } returns Car() // or you can return mockk() for example 

func()

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) }

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() }

Note: in case function return type is generic the information about actual type is erased. To make chained calls work additional information is required. Most of the times framework will catch the cast exception and do autohinting. But in the case it is explicitly needed just place hint before calls.

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

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),
    direction = Direction.NORTH
  )
} answers {
  println(slot.captured)

  Outcome.RECORDED
}


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

  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()) }

Verification atLeast, atMost or exactly times

You can check call count with 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

Verification order

verifyAll verifies that all calls happened without checking it's order. verifySequence verifies that the exact sequence happened and verifyOrder that calls happened in order. wasNot Called verifies that mock or 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
}

Returning nothing

If the function is returning Unit(i.e. no return value) you still need to specify null return value:

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

val obj = mockk<MockedClass>()

// all 3 are actually acceptable and doing the same
every { obj.sum(any(), 1) } answers { nothing }
every { obj.sum(any(), 2) } returns null
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 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 a 3 cases of extension function:

class wide
object wide
module wide

In case of object and class you can mock extension function just by creating 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 function you need to build staticMockk(...) with argument specifying module class name. For example "pkg.FileKt" for module "File.kt" in "pkg" package

data class Obj(val value: Int)

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

staticMockk("pkg.FileKt").use {
    every {
        Obj(5).extensionFunc()
    } returns 11

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

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

More 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()

DSL tables

Here are few tables helping to master the DSL.

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 values is null
`isNull(inverse=true)`	checks if values is not null
`ofType(type)`	checks if values belongs to the type
`match { it.startsWith("string") }`	matches via passed predicate
`coMatch { it.startsWith("string") }`	matches via passed coroutine predicate
`matchNullable { it?.startsWith("string") }`	matches nullable value via passe predicate
`coMatchNullable { it?.startsWith("string") }`	matches nullable value via passed coroutine predicate
`eq(value)`	matches if value is equal to the provided via deepEquals function
`refEq(value)`	matches if value is equal to the provided via reference comparation
`cmpEq(value)`	matches if value is equal to the provided via compareTo function
`less(value)`	matches if value is less to the provided via compareTo function
`more(value)`	matches if value is more to the provided via compareTo function
`less(value, andEquals=true)`	matches if value is less or equals to the provided via compareTo function
`more(value, andEquals=true)`	matches if value is more or equals to the provided via compareTo function
`and(left, right)`	combines two matchers via logical and
`or(left, right)`	combines two matchers via 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 lambda
`captureCoroutine()`	captures coroutine
`invoke(...)`	calls matched argument
`coInvoke(...)`	calls matched argument for coroutine
`hint(cls)`	hints next return type in case it's got erased

Few special matchers available in verification mode only:

Matcher	Description
`run { code }`	matches any value and allows to execute some code
`runNullable { code }`	matches any nullable value and allows to execute some code
`coRun { code }`	matches any value and allows to execute some coroutine code
`coRunNullable { code }`	matches any nullable value and allows to execute some coroutine code
`assert(msg) { predicate }`	matches any value and checks the assertion
`assertNullable(msg) { predicate }`	matches any nullable value and checks the assertion
`coAssert(msg) { predicate }`	matches any value and checks the coroutine assertion
`coAssertNullable(msg) { predicate }`	matches any nullable value and checks the coroutine assertion

Validators

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

Answers

Answer	Description
`returns value`	specify that matched call returns one specified value
`returnsMany list`	specify that matched call returns value from the list, returning each time next element
`throws ex`	specify that matched call throws an exception
`answers { code }`	specify that matched call answers with code block scoped with `answer scope`
`coAnswers { code }`	specify that matched call answers with coroutine code block with `answer scope`
`answers answerObj`	specify that matched call answers with Answer object
`answers { nothing }`	specify that matched call answers null
`just Runs`	specify that matched call is returning Unit (returns null)

Answer scope

Parameter	Description
`call`	a call object that consists of invocation and matcher
`invocation`	contains information regarding actual function invoked
`matcher`	contains information regarding matcher used to match invocation
`self`	reference the object invocation made
`method`	reference to the function invocation made
`args`	reference to 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 the list
`lambda<...>().invoke()`	call captured lambda
`coroutine<...>().coInvoke()`	call captured coroutine
`nothing`	null value for returning nothing as an answer

Getting Help

To ask questions, please use stackoverflow or gitter.

Chat/Gitter: https://gitter.im/mockk-io/Lobby
Stack Overflow: http://stackoverflow.com/questions/tagged/mockk

To report bugs, please use the GitHub project.

Project Page: https://github.com/oleksiyp/mockk
Reporting Bugs: https://github.com/oleksiyp/mockk/issues

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