Getting Started¶

Installation¶

Add the some library to your test dependencies. It is available on Maven Central.

Replace {version} with the latest release shown in the badge above.

Gradle (Kotlin DSL)Gradle (Groovy)Maven

testImplementation("dev.appoutlet:some:{version}")

testImplementation 'dev.appoutlet:some:{version}'

<dependency>
  <groupId>dev.appoutlet</groupId>
  <artifactId>some</artifactId>
  <version>{version}</version>
  <scope>test</scope>
</dependency>

kotlin-reflect is included as a transitive dependency — you don't need to declare it separately.

Usage¶

The simplest way to use Some is with the top-level some<T>() function:

import dev.appoutlet.some.some

data class User(val name: String, val age: Int)

val user = some<User>()
// User(name=xvqkpmnz, age=42)

It works with nested data classes, collections, and sealed classes — everything is resolved automatically without configuration:

data class Address(val street: String, val city: String)
data class Person(val name: String, val address: Address)

val person: Person = some<Person>()
val users: List<User> = some<List<User>>()

sealed class PaymentMethod {
    data class Card(val last4: String) : PaymentMethod()
    data class BankTransfer(val iban: String) : PaymentMethod()
    object Cash : PaymentMethod()
}

val payment: PaymentMethod = some<PaymentMethod>()

Using it in a test¶

Here's how Some fits into a typical JUnit 5 test. Instead of hand-crafting test data, you generate a realistic fixture with some<T>() and pass it to the code under test:

class WelcomeEmail {
    fun render(user: User) = "Hi ${user.name}, welcome! Verify your email at ${user.email}."
}

class WelcomeEmailTest {
    private val email = WelcomeEmail()

    @Test
    fun `render includes user name and email in the message`() {
        // Create the object that will be used
        val user = some<User>()

        // Pass the generated object on the function you want to test
        val message = email.render(user)

        // Do the assertions you would normally do, using your favourite assertion library
        assertTrue(user.name in message)
        assertTrue(user.email in message)
    }
}

Basic configuration¶

When you need control over the generated data, pass a config lambda to some. The seed guarantees reproducibility, StringStrategy.Readable makes failures easier to debug, and CollectionStrategy(2..4) limits list sizes to a known range:

val user = some<User> {
    stringStrategy = StringStrategy.Readable
}
// User(name=string-1234, age=17)

val users = some<List<User>> {
    collectionStrategy = CollectionStrategy(2..4)
}
// [User(name=string-1234, age=17), User(name=string-5678, age=23)]

For more configuration use cases and details, see the Configuration overview.

Requirements¶

Kotlin 2.3.0+ — required for typeOf<T>() and other type introspection APIs
JVM 21+ — Some is JVM-only; Android and Kotlin/Native are not currently supported