Features

The Kotlin plugin helps you take full advantage of Kotlin's concise, safe, and pragmatic nature when generating test fixtures.

What the Kotlin Plugin provides

• PrimaryConstructorArbitraryIntrospector as the default introspector — generates Kotlin classes using their primary constructor
• Extension functions — giveMeOne<T>(), giveMeKotlinBuilder<T>() for idiomatic Kotlin usage
• Kotlin DSL Exp — type-safe property references (KotlinClass::field) instead of string-based paths
• Kotlin instantiateBy DSL — choose which constructor or factory method to use

Dependencies

:::tip Recommended Use fixture-monkey-starter-kotlin for new projects. It includes fixture-monkey-starter and fixture-monkey-jakarta-validation out of the box. :::

Gradle

testImplementation("com.navercorp.fixturemonkey:fixture-monkey-starter-kotlin:1.2.3")

Maven

<dependency>
  <groupId>com.navercorp.fixturemonkey</groupId>
  <artifactId>fixture-monkey-starter-kotlin</artifactId>
  <version>1.2.3</version>
  <scope>test</scope>
</dependency>

If you only need the core Kotlin support without the starter bundle:

testImplementation("com.navercorp.fixturemonkey:fixture-monkey-kotlin:1.2.3")

Plugin Setup

val fixtureMonkey = FixtureMonkey.builder()
    .plugin(KotlinPlugin())
    .build()

Quick Example

KotlinquickExample()

KotlinPluginFeaturesTest.kt

// given
val product: Product = fixtureMonkey.giveMeOne()

// then
then(product).isNotNull

With customization using type-safe property references:

KotlincustomizeWithTypeSafeReferences()

KotlinPluginFeaturesTest.kt

// when
val custom = fixtureMonkey.giveMeKotlinBuilder<Product>()
	.setExp(Product::name, "Fixture Monkey")
	.setExp(Product::price, 29_900L)
	.sizeExp(Product::options, 3)
	.sample()

// then
then(custom.name).isEqualTo("Fixture Monkey")
then(custom.price).isEqualTo(29_900L)
then(custom.options).hasSize(3)

Extension Functions

The Kotlin plugin provides extension functions that leverage Kotlin's reified type parameters, so you don't need to pass Class<T> explicitly:

Extension Function	Description
giveMeOne<T>()	Generate a single random instance
giveMeBuilder<T>()	Get an ArbitraryBuilder<T> (string-based API)
giveMeKotlinBuilder<T>()	Get a Kotlin-aware builder with setExp, sizeExp etc.
giveMe<T>(count)	Generate a stream of random instances

// No need for Product::class.java
val product: Product = fixtureMonkey.giveMeOne()
val products: List<Product> = fixtureMonkey.giveMe<Product>(5).toList()
val builder = fixtureMonkey.giveMeKotlinBuilder<Product>()

Type-Safe Property References (Kotlin DSL Exp)

Instead of string-based path expressions like set("name", value), use Kotlin property references for compile-time safety:

// String-based (works but no compile-time check)
builder.set("name", "Fixture Monkey")

// Type-safe (compile error if property doesn't exist)
builder.setExp(Product::name, "Fixture Monkey")

For nested properties, use the into infix function:

KotlinnestedPropertyReference()

KotlinPluginFeaturesTest.kt

// when
val order = fixtureMonkey.giveMeKotlinBuilder<Order>()
	.setExp(Order::product into Product::name, "Fixture Monkey")
	.sample()

// then
then(order.product.name).isEqualTo("Fixture Monkey")

For Java classes (getter-based), use setExpGetter and intoGetter:

builder.setExpGetter(JavaProduct::getName, "Fixture Monkey")
builder.setExpGetter(
    JavaOrder::getProduct intoGetter JavaProduct::getName,
    "Fixture Monkey"
)

See Kotlin DSL Exp for the full reference.

Introspectors for Kotlin

The Kotlin plugin sets PrimaryConstructorArbitraryIntrospector as the default, which creates objects using Kotlin's primary constructor.

For projects that mix Kotlin and Java classes, use KotlinAndJavaCompositeArbitraryIntrospector:

val fixtureMonkey = FixtureMonkey.builder()
    .plugin(KotlinPlugin())
    .objectIntrospector(KotlinAndJavaCompositeArbitraryIntrospector())
    .build()

See Introspectors for Kotlin for details.