Error compiling Scala Test Case with org.scalatest.AnyFlatSpec

TEST ENVIRONMENT
<akka.version>2.6.16</akka.version>
<scala.version>2.12.10</scala.version>

org.scalatest
scalatest_2.12
3.2.10


com.typesafe.akka
akka-testkit_2.12
2.6.16

import akka.actor.ActorSystem
import akka.testkit.{ImplicitSender, TestKit}
import org.scalatest._
import flatspec._
import matchers._

abstract class BaseActorTest(val sys: String) extends TestKit(ActorSystem(sys)) with ImplicitSender
with AnyFlatSpec with should.Matchers with OptionValues with Inside with Inspectors

import akka.actor.ActorSystem
import com.typesafe.config.ConfigFactory
import org.specs2.matcher.ShouldMatchers

class ApplicationTest extends BaseActorTest(“Cluster”) with ShouldMatchers {

“a application dev should” should {
“be able to build frontend application” in {
val frontend = new FrontEndHttpApplication(“testrole”, Vector(SecondFrontEndRoute1), “testbackendrole”, “loadbalancer”)
val sys = ActorSystem(“Cluster”)
val defaultRouter = sys.actorSelection("/user/BackendRouter")
if (defaultRouter == None) fail(“Deafaut Router is not up”)
}
}
}

I have migrated scalaTest from 2.11 to 2.12. After that started getting following error when compiling above code.

ERROR - "ApplicationTest.scala:18: value in is not a member of string.

As per ScalaTest doc “in” is part of ScalaTest Jar.
https://www.scalatest.org/scaladoc/3.2.9/org/scalatest/flatspec/AnyFlatSpec.html

Please suggest…