Kotlin shared companion object across junit tests - mongodb

Question

I have an integration test where I start an embedded MongoDB as a companion object. I want to reuse this piece of code and I am not sure if inheritance is the way to go (if possible).
It is a Spring Boot application:
This is my test:
#RunWith(SpringRunner::class)
#SpringBootTest
class RequestRepositoryTest {
#Autowired lateinit var requestRepository: RequestRepository
companion object {
private val starter = MongodStarter.getDefaultInstance()
private var _mongod: MongodProcess? = null
private var _mongo: MongoClient? = null
#BeforeClass
#JvmStatic fun beforeTest(){
val port = 27017
val _mongodExe = starter.prepare(MongodConfigBuilder()
.version(Version.Main.DEVELOPMENT)
.net(Net("localhost", port, Network.localhostIsIPv6()))
.build())
_mongod = _mongodExe.start()
_mongo = MongoClient("localhost", port)
}
#AfterClass
#JvmStatic fun afterTest(){
_mongod?.stop()
}
}
#Test
fun store() {
val id = requestRepository.store(Request(requestId = "123"))
assertNotNull(id)
}
}
My repository class:
#Repository
class RequestRepository #Autowired constructor(val datastore: Datastore)
{
fun store(request : Request) : String =
datastore.save(request).id.toString()
}
So my question is which is the 'correct' way to go about this in Kotlin.
Update edit: As an external object the test now looks a lot cleaner and the JUnit external resource is completely reusable across test classes:
Thanks #Lovis
#RunWith(SpringRunner::class)
#SpringBootTest
class RequestRepositoryTest {
companion object {
#ClassRule
#JvmField
val mongoServer = MongoServer
}
#Autowired lateinit var requestRepository: RequestRepository
#Test
fun store() {
val id = requestRepository.store(Request(requestId = "123"))
assertNotNull( id )
assertTrue { ObjectId.isValid(id) }
}
}

Answer 1

You should be able to achieve what you want using jUnit's #ClassRule and ExternalResource. No Kotlin magic needed :-)
Define an object in a separate File:
object MongoServer : ExternalResource() {
#Throws(Throwable::class)
override fun before() {
// before class
}
override fun after() {
// after class
}
}
Then use it within each test:
companion object {
#ClassRule
#JvmField
val mongoServer = MongoServer
}
The ClassRule annotation does the trick here, the companion object is necessary to make it static and the #JvmField annotation is necessary to make the field public. Those are restrictions by jUnit's rule system.