MocKMP

= MocKMP :toc: macro :toclevels: 2 :idprefix: :idseparator: - :icons: font :source-highlighter: highlight.js

Compile-time mocks and fakes for Kotlin Multiplatform tests — generated by a KSP processor, not by reflection.

MocKMP turns a plain interface or abstract class into a mock or a fake for your tests. You ask for what a test needs with an annotation — @Mock, @Fake, @UsesMocks, @UsesFakes — and a KSP processor generates the implementation, ready to inject.

class MyTest : TestsWithMocks() { override fun setUpMocks() = mocker.injectMocks(this)

@Mock lateinit var view: View
@Fake lateinit var model: Model

val controller by withMocks { Controller(view = view, firstModel = model) }

@Test fun controllerTest() {
    every { view.render(isAny()) } returns true
    controller.start()
    verify { view.render(model) }
}

No reflection, no dynamic proxies, no "relaxed" mode papering over a call nobody mocked. An interface, a generated implementation, and a compiler that rejects a mock or a fake for a type that can't be one.

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== Why MocKMP

Compile-time, not reflection. A KSP processor generates a real class implementing the interface or abstract class you asked to mock or fake, so it behaves identically on every target — including the ones with no runtime reflection at all, like iOS, JS and Wasm.

Mocking and faking answer different questions. A mock's behaviour is defined per test, and every call on it can be verified; a fake's data is inert and zero-valued, and nothing about it is checked. Reach for a fake when a collaborator only needs to exist, and a mock when the test needs to configure or verify it.

Nothing is generated until you ask for it. @UsesMocks / @UsesFakes — or a @Mock / @Fake property — requests exactly the types a given test needs, so an interface used across a large codebase doesn't grow generated code everywhere it's declared, only where it's actually mocked or faked.

Injection kills the constructor boilerplate. Annotate properties @Mock or @Fake and call mocker.injectMocks(this); inherited properties are injected too, so a shared base test class works exactly as if its mocks had been declared locally.

The TestsWithMocks helper collapses the ceremony further. Inherit it and get a Mocker, an automatic reset before every test, withMocks property delegates rebuilt fresh each time, and every / everySuspending / verify / verifyWithSuspend callable without the mocker. prefix.

Constraints read the same in a definition and in a verification. isAny, isEqual, isNotNull, isInstanceOf, and any custom constraint you write with isValid, work identically whether they appear inside every or inside verify — one matcher vocabulary, not two.

Multiplatform, with no platform-specific surprises. mockmp-runtime targets every platform MocKMP supports and behaves the same on each of them.

== Installation

WARNING: Version 2.0 brings compatibility with Kotlin 2.0, but with breaking changes. If you're on version 1.17, see the https://kosi-libs.org/mockmp/2.0/migration/1to2.html[1.x to 2.x migration guide].

WARNING: Version 3.0 brings compatibility with AGP 9, but becomes incompatible with AGP 8 or earlier. Only update to MocKMP 3.0 if you are also updating to AGP 9 — if you're on version 2.1, see the https://kosi-libs.org/mockmp/3.0/migration/2to3.html[2.x to 3.x migration guide].

Apply the Gradle plugin to your Kotlin/Multiplatform module, then enable it on the test source sets you want mocks and fakes generated for:

plugins { kotlin("multiplatform") id("com.google.devtools.ksp") // <1> id("org.kodein.mock.mockmp") version "{version}" // <2> }

kotlin { // Your Kotlin/Multiplatform configuration }

<1> KSP hosts the MocKMP processor. <2> The MocKMP Gradle plugin — it wires the runtime and the processor for you, so there is no dependency to add by hand. <3> Configured after the kotlin { } block, so the plugin can see your targets. withHelper() also pulls in the TestsWithMocks helper class.

The plugin applies just as well to a single-target kotlin("jvm") or kotlin("android") project.

== Read more

See https://kosi-libs.org/mockmp/[MocKMP Documentation].