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Test Fixtures (JVM)

Share generated fakes across JVM modules using Gradle’s built-in test fixtures plugin — no collector module needed.

JVM Only

This feature requires the java-test-fixtures Gradle plugin, which is only available for JVM and Android projects. For KMP multi-module projects, use the Collector Module approach instead.

Test Fixtures vs Collector Module

Test Fixtures Collector Module
Platform JVM / Android only KMP + JVM + Android
Extra module needed? No Yes (:module-fakes)
Setup complexity Minimal (2 lines) Moderate (new module + config)
Consumer dependency testFixtures(projects.core) implementation(projects.core.fakes)
Best for JVM multi-module projects KMP projects, Maven publishing

Setup

Step 1: Configure the Producer Module

Apply the java-test-fixtures plugin and enable useGradleTestFixtures:

// core/build.gradle.kts
plugins {
    kotlin("jvm")
    `java-test-fixtures`
    alias(libs.plugins.fakt)
}

fakt {
    useGradleTestFixtures.set(true)
}

Define your @Fake annotated types as usual:

// core/src/main/kotlin/com/example/core/UserRepository.kt
@Fake
interface UserRepository {
    fun findById(id: String): User?
    fun save(user: User): User
    fun delete(id: String): Boolean
}

Build the module to generate fakes:

./gradlew :core:build

Verify fakes are generated in the testFixtures directory:

core/build/generated/fakt/testFixtures/kotlin/
└── com/example/core/
    └── FakeUserRepositoryImpl.kt

Step 2: Consume in Another Module

In the consumer module, add a testFixtures() dependency — no Fakt plugin needed:

// app/build.gradle.kts
plugins {
    kotlin("jvm")
}

dependencies {
    implementation(projects.core)
    testImplementation(testFixtures(projects.core))
}

Use the generated fakes in tests:

// app/src/test/kotlin/com/example/app/UserServiceTest.kt
class UserServiceTest {
    @Test
    fun `GIVEN user exists WHEN getUser THEN returns user`() {
        val repo = fakeUserRepository {
            findById { id -> User(id, "Alice") }
        }
        val service = UserService(repo)

        val result = service.getUser("1")

        assertEquals("Alice", result?.name)
    }
}

How It Works

  1. Fakt detects java-test-fixtures plugin and useGradleTestFixtures.set(true)
  2. Generated fakes go to build/generated/fakt/testFixtures/kotlin/ instead of test/
  3. The testFixtures source set is configured to include the generated directory
  4. The module’s own tests can use the fakes (Gradle makes testFixtures visible to test automatically)
  5. Other modules import fakes via testFixtures(project(":core")) — standard Gradle mechanism

Validation

If useGradleTestFixtures is enabled but the java-test-fixtures plugin is not applied, Fakt emits a warning and falls back to the default test source set:

Fakt: useGradleTestFixtures is enabled but the 'java-test-fixtures' plugin
is not applied. Add `java-test-fixtures` to your plugins block:
  plugins {
      `java-test-fixtures`
  }
Falling back to default 'test' source set.

Sample Project

See samples/jvm-test-fixtures/ for a working multi-module example with:

  • core/ — Producer with interface, abstract class, and open class
  • app/ — Consumer using fakes from core’s testFixtures

Next Steps