Fixing "too many open files" error in tests

build.sbt

@@ -3,7 +3,7 @@ import scala.util.Try
 name := "scorex-core"
 
 lazy val commonSettings = Seq(
-  scalaVersion := "2.12.3",
+  scalaVersion := "2.12.10",
   resolvers += Resolver.sonatypeRepo("public"),
   wartremoverErrors ++= Seq(
     Wart.Recursion,

src/test/scala/scorex/network/NetworkControllerSpec.scala

@@ -336,6 +336,7 @@ class TestPeer(settings: ScorexSettings, networkControllerRef: ActorRef, tcpMana
   private val messageSpecs = Seq(GetPeersSpec, peersSpec)
   private val messagesSerializer = new MessageSerializer(messageSpecs, settings.network.magicBytes)
 
+  @SuppressWarnings(Array("org.wartremover.warts.Null"))
   private var connectionHandler: ActorRef = _
 
   /**

testkit/src/main/scala/scorex/testkit/utils/FileUtils.scala

@@ -1,8 +1,6 @@
 package scorex.testkit.utils
 
-import java.io.IOException
-import java.nio.file.attribute.BasicFileAttributes
-import java.nio.file.{FileVisitResult, Files, Path, SimpleFileVisitor}
+import java.nio.file.Path
 
 import org.scalacheck.Gen
 
@@ -36,20 +34,21 @@ trait FileUtils {
   }
 
   /**
-    * Recursively remove all files and directories in `root`
+    * Recursively remove all the files and directories in `root`
     */
   def remove(root: Path): Unit = {
-    Files.walkFileTree(root, new SimpleFileVisitor[Path] {
-      override def visitFile(file: Path, attrs: BasicFileAttributes): FileVisitResult = {
-        Files.delete(file)
-        FileVisitResult.CONTINUE
-      }
 
-      override def postVisitDirectory(dir: Path, exc: IOException): FileVisitResult = {
-        Files.delete(dir)
-        FileVisitResult.CONTINUE
+    @SuppressWarnings(Array("org.wartremover.warts.Recursion"))
+    def deleteRecursive(dir: java.io.File): Unit = {
+      for (file <- dir.listFiles) {
+        if (file.isDirectory){
+          deleteRecursive(file)
+        }
+        file.delete()
       }
-    })
+    }
+
+    deleteRecursive(root.toFile)
   }
 
   private def createTempDirForPrefix(prefix: String): java.io.File = {