Porting of "Simple example of testing with ZIO environment" to Kotlin

fx-test.kt

// Porting of https://gist.github.com/jdegoes/dd66656382247dc5b7228fb0f2cb97c8

typealias UserID = String
data class UserProfile(val name: String)

// The database module:
interface DatabaseService {
    suspend fun dbLookup(id: UserID): UserProfile
    suspend fun dbUpdate(id: UserID, profile: UserProfile)
}

// The logger module:
interface LoggerService {
    suspend fun logInfo(id: String)
}

// A concurrent-safe test database service, which uses a `Ref` to keep track
// of changes to the test database state:
class DatabaseTestService(val ref: Ref<ForIO, State>) : DatabaseService {

    data class State(val map: Map<UserID, UserProfile>, val ops: List<String>) {

        fun log(op: String): State = copy(ops = listOf(op) + ops)

        fun lookup(id: UserID): Tuple2<State, Option<UserProfile>> =
                Tuple2(log("Lookup($id)"), map.getOption(id))

        fun update(id: UserID, profile: UserProfile): State =
                copy(map = map.plus(id to profile)).log("Update($id, $profile)")

    }

    override suspend fun dbLookup(id: UserID): UserProfile =
            ref.modify { it.lookup(id) }.fix().suspended().orNull()!!

    override suspend fun dbUpdate(id: UserID, profile: UserProfile) =
            ref.update { it.update(id, profile) }.fix().suspended()

}

// A concurrent-safe test logger service, which uses a `Ref` to keep track
// of log output:
class LoggerTestService(val ref: Ref<ForIO, List<String>>) : LoggerService {

    override suspend fun logInfo(line: String) = ref.update { it.plus(line) }.fix().suspended()
}

interface Env : DatabaseService, LoggerService

// A helper function to run a test scenario, and extract out test data.
// This function can be used many times across many unit tests.
fun <A> testScenario(state: State, program: suspend Env.() -> A) : IO<Tuple3<Either<Throwable, A>, State, List<String>>> =
    IO.fx {

        val databaseRef = !ref { state }
        val loggerRef = !ref { emptyList<String>() }

        val env: Env = object : Env,
                DatabaseService by DatabaseTestService(databaseRef),
                LoggerService by LoggerTestService(loggerRef) {}

        val either = !attempt { env.program() }

        val dbState = !databaseRef.get()
        val loggerState = !loggerRef.get()

        Tuple3(either, dbState, loggerState)
    }

// An example program that uses database and logger modules:
suspend fun Env.lookedUpProfile(): UserProfile {
    val profile = dbLookup("abc")
    logInfo(profile.name)
    return profile
}

// Running a test scenario and unsafely executing it to see what happens:
fun main() {
    val program = testScenario(State(mapOf("abc" to UserProfile("testName")), emptyList()), Env::lookedUpProfile)
    val result = program.unsafeRunSync()
    println(result)
}

Thank you very much for taking the time to answer. It is indeed more similar / and a bit more straightforward. I'll try experimenting with it :)