Kotlin DSL Exp

Fixture Monkey utilizes Kotlin’s DSL feature to ensure type-safety with expressions. Let’s explore how we can employ Kotlin Exp instead of the standard Java String Expression.

Referencing a property

Suppose we have an object structure similar to the one described earlier, written in both Java and Kotlin:

@Value
public class JavaClass {
    String field;

    List<String> list;

    Nested nestedObject;

    List<Nested> nestedObjectList;

    @Value
    public static class Nested {
        String nestedField;
    }
}

data class KotlinClass(
  val field: String,

  val list: List<String>,

  val nestedObject: Nested,

  val nestedObjectList: List<Nested>
) {
  data class Nested(
    val nestedField: String
  )
}

To use Kotlin Exp to reference a property, you need to use the Exp or ExpGetter suffix to the normal Fixture Customization APIs.

Let’s look at the example of customizing properties with Kotlin Exp using setExp() and setExpGetter().

@Test
fun test() {
    // given
    val fixtureMonkey = FixtureMonkey.builder()
        .plugin(KotlinPlugin())
        .plugin(JacksonPlugin())
        .build()

    // when
    val javaClass = fixtureMonkey.giveMeBuilder<JavaClass>()
        .setExpGetter(JavaClass::getField, "field")
        .sample()

    val kotlinClass = fixtureMonkey.giveMeBuilder<KotlinClass>()
        .setExp(KotlinClass::field, "field")
        .sample()

    // then
    then(javaClass.field).isEqualTo("field")
    then(kotlinClass.field).isEqualTo("field")
}

In the code above, we can see that we are using Kotlin’s method reference to select a property.

setExp() takes an argument of type KProperty, while setExpGetter() takes an argument of type KFunction.

If the class is defined in Java, the expression (e.g. JavaClass::getField) is of type KFunction because it is a reference to a Java getter. Therefore you can only use the setExpGetter() method.

If it is a Kotlin class, the expression (e.g. KotlinClass::field) is KProperty, so you should use setExp().

Referencing a nested property

To access a nested field, the infix functions into and intoGetter are used. into takes a parameter of type KProperty, while intoGetter takes a parameter of type KFunction.

@Test
fun test() {
    // given
    val fixtureMonkey = FixtureMonkey.builder()
        .plugin(KotlinPlugin())
        .plugin(JacksonPlugin())
        .build()

    // when
    val javaClass = fixtureMonkey.giveMeBuilder<JavaClass>()
        .setExp(JavaClass::getNestedObject intoGetter JavaClass.Nested::getNestedField, "nestedField")
        .sample()

    val kotlinClass = fixtureMonkey.giveMeBuilder<KotlinClass>()
        .setExp(KotlinClass::nestedObject into KotlinClass.Nested::nestedField, "nestedField")
        .sample()

    then(javaClass.nestedObject.nestedField).isEqualTo("nestedField")
    then(kotlinClass.nestedObject.nestedField).isEqualTo("nestedField")
}

An expression that contains an into or intoGetter operator becomes an ExpressionGenerator type in fixture monkey. Both setExp() and setExpGetter()) are defined to take ExpressionGenerator types as arguments, so you can use both.

Selecting Properties Using Kotlin DSL Expressions

Selecting the root object:
  • Currently Not Supported
Selecting a specific field: 
JavaClass::getField // java class

KotlinClass::field // kotlin class
Selecting a nested field: 
JavaClass::getNestedObject intoGetter JavaClass.Nested::getNestedField // java class

KotlinClass::nestedObject into KotlinClass.Nested::nestedField // kotlin class
Selecting the n-th element of a collection: 
JavaClass::getNestedObjectList["0"] // java class

KotlinClass::nestedObjectList["0"] // kotlin class
Selecting all elements of a collection: 
JavaClass::getNestedObjectList["*"] // java class

KotlinClass::nestedObjectList["*"] // kotlin class
Combining expressions to select a nested field: 
JavaClass::getNestedObject intoGetter JavaClass.Nested::getNestedField // java class

KotlinClass::nestedObject into KotlinClass.Nested::nestedField // kotlin class
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