headsvk/defaults

Kotlin Data Class Defaults

Simple instantiation of data classes in your tests.

Installation

repositories {
    maven { url("https://jitpack.io") }
}

dependencies {
    testImplementation("com.github.headsvk:defaults:${version}")
}

Usage

Let's say we have following nested data classes (coming from an api for example):

data class Foo(
    val string: String,
    val optionalInt: Int?,
)
data class Bar(
    val locale: Locale,
    val foo: Foo,
)
data class Baz(
    val int: Int,
    val double: Double,
    val bar: Bar,
)

We don't want to provide default values in constructors to enforce full initialization in production code, but we can easily instantiate Baz in tests by:

register(Locale.US)                 // Register a default value for a class
register(Double.POSITIVE_INFINITY)  // Register a custom primitive value
val baz = default<Baz>()            // Create Baz with default values or nulls

Then baz has following values:

assertEquals(Baz(
    int = 0,
    double = Double.POSITIVE_INFINITY,
    bar = Bar(
        locale = Locale.US,
        foo = Foo(
            string = "",
            optionalInt = null,
        ),
    ),
), baz) 

The created instance of Baz is not a mock thus data class functions such as equals, toString and copy work as expected.

Limitations

Registering defaults for generic classes is not supported but all kotlin collections default to empty.

The library depends on the full kotlin-reflect JVM library so support for Kotlin Multiplatform is not currently possible.