Test all enums implementing the marker interface

Question

I have the empty interface interface HavingUniqueValues(val v: Int) {} and some enums like enum class EnumName(override val v: Int) : HavingUniqueValues.

I want the elements in each enum have unique v-values but I can mistype the values. So I need a test.

1. Is it possible to create a test where the interface implementations are saved as a List manually and the test checks if all the implementations in the List meet the requirement?
2. If yes: is it possible to create a function that returns the List of all implementations in the specified package to use it in the test?

Answer 1

Take a look at the Reflections library which might aid you with this.

You should be able to get all subtypes of HavingUniqueValues:

val subjects: Set<Class<out HavingUniqueValues>> =
        Reflections("your.package").getSubTypesOf(HavingUniqueValues::class.java)

Now, this will result in a Set of all enum classes that implement HavingUniqueValues. You can iterate all of their values to know if they are unique or not:

subjects.forEach { enumClass ->
    assertEquals(
            enumClass.enumConstants.size,
            enumClass.enumConstants.map(HavingUniqueValues::v).toSet().size
    )
}

I used toSet() here to drop all non-inuque values.

This will pass the test:

enum class EnumName(override val v: Int) : HavingUniqueValues { ONE(1), TWO(2), THREE(3) }

This will not pass the test:

enum class EnumName(override val v: Int) : HavingUniqueValues { ONE(1), TWO(2), THREE(2) }