Stub

0.8.0indexed

Compiler-plugin mocking that generates compile-time stubs with an expressive DSL, argument matchers, coroutine support, final-class mocking and zero runtime reflection for type-safe testing.

AndroidJSJVMNative·yarokovisty/Stub

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Stub

A lightweight mocking framework for Kotlin Multiplatform. Stub generates mock implementations at compile time using a Kotlin compiler plugin — no reflection, no manual mock classes. Works on JVM, Android, iOS, and JS.

Core DSL

API	Description
`stub<T>()`	Create a stub for any interface or final class
`every { } returns`	Configure a return value
`every { } throws`	Configure an exception
`every { } answers { }`	Compute a return value dynamically
`verify { }`	Assert a method was called
`any()`	Match any argument
`eq(value)`	Match by equality
`coEvery { }`	`every` for suspend functions

Usage

Basic example

import org.yarokovisty.stub.dsl.*
import kotlin.test.Test
import kotlin.test.assertEquals

  {
    : String
}

  {

      repository: UserRepository = stub()

    
     {
        every { repository.findById() } returns 

        assertEquals(, repository.findById())

        verify { repository.findById() }
    }
}

Argument matchers

// Match any arguments
every { repository.findById(any()) } returns "Unknown"

// Override specific cases — last registered wins
every { repository.findById(eq(1)) } returns "Alice"

repository.findById(1)   // "Alice"
repository.findById(999) // "Unknown"

Final class mocking

No open keyword needed — the compiler plugin handles it:

class DataSource {
    fun load(): String = "real"
}

val dataSource: DataSource = stub()
every { dataSource.load() } returns "mocked"

Suspend functions

import kotlinx.coroutines.test.runTest

interface ApiService {
    suspend fun fetchData(): String
}

@Test
fun testSuspend() = runTest {
    val api: ApiService = stub()

    coEvery { api.fetchData() } returns "async result"

    assertEquals("async result", api.fetchData())
    coVerify { api.fetchData() }
}

Clearing state

clearStubs(repository)       // Clear answers and call history
clearInvocations(repository) // Clear call history only

Installation

Apply the compiler plugin and add the DSL dependency:

build.gradle.kts

plugins {
    id("io.github.yarokovisty.stub.compiler") version "<version>"
}

kotlin {
    sourceSets {
        commonTest.dependencies {
            implementation("io.github.yarokovisty:stub-dsl:<version>")
            implementation("io.github.yarokovisty:stub-runtime:<version>")
            implementation(libs.kotlin.test)
            implementation(libs.kotlinx.coroutines.test) // for coEvery/coVerify
        }
    }
}