Getting started

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

Gradle/Maven dependency

<table> <thead><tr><th>Approach</th><th>Instruction</th></tr></thead> <tr> <td><img src="doc/gradle.png" alt="Gradle"/></td> <td> <pre> testImplementation "io.mockk:mockk:${mockkVersion}" </pre> </td> </tr> <tr> <td><img src="doc/gradle.png" alt="Gradle"/> (Kotlin DSL)</td> <td> <pre>testImplementation("io.mockk:mockk:${mockkVersion}")</pre> </td> </tr> <tr> <td><img src="doc/maven.png" alt="Maven"/></td> <td> <pre> <dependency> <groupId>io.mockk</groupId> <artifactId>mockk-jvm</artifactId> <version>${mockkVersion}</version> <scope>test</scope> </dependency> </pre> </td> </tr> <tr> <td><a href="ANDROID.html"><img align="top" src="doc/robot-small.png" height="20" alt="android"/> Unit</a></td> <td> <pre> testImplementation "io.mockk:mockk-android:${mockkVersion}" testImplementation "io.mockk:mockk-agent:${mockkVersion}" </pre> </td> </tr> <tr> <td><a href="ANDROID.html"><img align="top" src="doc/robot-small.png" height="20" alt="android"/> Instrumented</a></td> <td> <pre> androidTestImplementation "io.mockk:mockk-android:${mockkVersion}" androidTestImplementation "io.mockk:mockk-agent:${mockkVersion}" </pre> </td> </tr> </table>

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)

See the "Features" section below for more detailed examples.

BDD style (optional)

For teams using Behavior-Driven Development, MockK provides BDD-style aliases

testImplementation "io.mockk:mockk:${mockkVersion}"
testImplementation "io.mockk:mockk-bdd:${mockkVersion}"

androidTestImplementation "io.mockk:mockk-android:${mockkVersion}"
androidTestImplementation "io.mockk:mockk-bdd-android:${mockkVersion}"

BDD aliases

| Standard MockK | BDD style | |----------------|-----------| | every { ... } | given { ... } | | coEvery { ... } | coGiven { ... } | | verify { ... } | then { ... } | | coVerify { ... } | coThen { ... } |

Spring support

springmockk introduced in official Spring Boot Kotlin tutorial

Quarkus support

quarkus-mockk adds support for mocking beans in Quarkus. Documentation can be found here

Kotlin version support

From version 1.13.0 MockK supports Kotlin 1.4 and higher

Known issues

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)
Inline functions cannot be mocked: see the discussion on this issue
Spies, mockkStatic may not work on JDK 16+; InaccessibleObjectException/IllegalAccessException: read more here
Using a spy with a suspending function will give unexpected test results

Table of contents:

auto-gen TOC: {:toc}

Examples, guides & articles

Kotlin Academy articles <img src="https://cdn-images-1.medium.com/letterbox/47/47/50/50/1*FUXqI88mttV_kV8aTrKjOg.png?source=logoAvatar-1f9f77b4b3d1---e57b304801ef" width="20px" />

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.

Japanese guides and articles

Chinese guides and articles

Korean guides and articles

Features

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 injects 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 initialized somehow. 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.

@InjectMockKs dependency order

If multiple @InjectMockKs properties depend on each other via constructor parameters, initialization order matters. By default, MockK processes them in reflection order; to resolve dependencies deterministically, enable dependency order:

@Before
fun setUp() = MockKAnnotations.init(this, useDepende

Mockk

Install / Use

README