even though i’m creating the modules as shown in the documentation:

@JvmField
  @RegisterExtension
  val koinTestExtension = KoinTestExtension.create {
      modules(
        module {
          single {
            println("creating vertx instance")
            Vertx.vertx()
            println("done creating vertx intstance")
          }
        ...
   }

Your single is returning Unit because of the println. Remove it or use Vertx.vertx().also { println(“…”) }

🤦