diff --git a/akka-multi-node-testkit/src/main/mima-filters/2.5.22.backwards.excludes b/akka-multi-node-testkit/src/main/mima-filters/2.5.22.backwards.excludes
new file mode 100644
index 0000000000..1209e72ec2
--- /dev/null
+++ b/akka-multi-node-testkit/src/main/mima-filters/2.5.22.backwards.excludes
@@ -0,0 +1,2 @@
+ProblemFilters.exclude[DirectMissingMethodProblem]("akka.remote.testkit.PerfFlamesSupport.*")
+ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.remote.testkit.PerfFlamesSupport.runPerfFlames")
diff --git a/akka-testkit/src/main/scala/akka/testkit/TestActorRef.scala b/akka-testkit/src/main/scala/akka/testkit/TestActorRef.scala
index acf6143f59..368ede795a 100644
--- a/akka-testkit/src/main/scala/akka/testkit/TestActorRef.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/TestActorRef.scala
@@ -6,10 +6,13 @@ package akka.testkit
 
 import akka.actor._
 import java.util.concurrent.atomic.AtomicLong
+
 import akka.dispatch._
+
 import scala.concurrent.Await
 import scala.reflect.ClassTag
 import akka.pattern.ask
+import com.github.ghik.silencer.silent
 
 /**
  * This special ActorRef is exclusively for use during unit testing in a single-threaded environment. Therefore, it
@@ -18,6 +21,7 @@ import akka.pattern.ask
  *
  * @since 1.1
  */
+@silent // 'early initializers' are deprecated on 2.13 and will be replaced with trait parameters on 2.14. https://github.com/akka/akka/issues/26753
 class TestActorRef[T <: Actor](_system: ActorSystem, _props: Props, _supervisor: ActorRef, name: String) extends {
   val props =
     _props.withDispatcher(
diff --git a/akka-testkit/src/main/scala/akka/testkit/TestEventListener.scala b/akka-testkit/src/main/scala/akka/testkit/TestEventListener.scala
index 8b038aaf20..b8dfe038f8 100644
--- a/akka-testkit/src/main/scala/akka/testkit/TestEventListener.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/TestEventListener.scala
@@ -540,6 +540,7 @@ final case class DeadLettersFilter(val messageClass: Class[_])(occurrences: Int)
  * }
  * </code></pre>
  */
+@ccompatUsedUntil213
 class TestEventListener extends Logging.DefaultLogger {
   import TestEvent._
 
diff --git a/akka-testkit/src/main/scala/akka/testkit/TestKit.scala b/akka-testkit/src/main/scala/akka/testkit/TestKit.scala
index c5afdbff68..e89ee0343c 100644
--- a/akka-testkit/src/main/scala/akka/testkit/TestKit.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/TestKit.scala
@@ -15,12 +15,12 @@ import scala.concurrent.Await
 import scala.concurrent.duration._
 import scala.reflect.ClassTag
 import scala.util.control.NonFatal
-
 import akka.actor._
 import akka.util.{ BoxedType, Timeout }
 import akka.actor.IllegalActorStateException
 import akka.actor.DeadLetter
 import akka.actor.Terminated
+import com.github.ghik.silencer.silent
 
 object TestActor {
   type Ignore = Option[PartialFunction[Any, Boolean]]
@@ -919,6 +919,7 @@ trait TestKitBase {
  *
  * @since 1.1
  */
+@silent // 'early initializers' are deprecated on 2.13 and will be replaced with trait parameters on 2.14. https://github.com/akka/akka/issues/26753
 class TestKit(_system: ActorSystem) extends { implicit val system = _system } with TestKitBase
 
 object TestKit {
diff --git a/akka-testkit/src/main/scala/akka/testkit/package.scala b/akka-testkit/src/main/scala/akka/testkit/package.scala
index 7e0b55b3a1..64e4ccb037 100644
--- a/akka-testkit/src/main/scala/akka/testkit/package.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/package.scala
@@ -12,6 +12,7 @@ import scala.collection.immutable
 import java.util.concurrent.TimeUnit.MILLISECONDS
 
 package object testkit {
+  @ccompatUsedUntil213
   def filterEvents[T](eventFilters: Iterable[EventFilter])(block: => T)(implicit system: ActorSystem): T = {
     def now = System.currentTimeMillis
 
diff --git a/akka-testkit/src/test/scala/akka/testkit/AkkaSpecSpec.scala b/akka-testkit/src/test/scala/akka/testkit/AkkaSpecSpec.scala
index 678f8f55ab..50c753a083 100644
--- a/akka-testkit/src/test/scala/akka/testkit/AkkaSpecSpec.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/AkkaSpecSpec.scala
@@ -5,16 +5,18 @@
 package akka.testkit
 
 import language.postfixOps
-
 import org.scalatest.WordSpec
 import org.scalatest.Matchers
 import akka.actor._
 import com.typesafe.config.ConfigFactory
+
 import scala.concurrent.Await
 import scala.concurrent.duration._
 import akka.actor.DeadLetter
 import akka.pattern.ask
+import com.github.ghik.silencer.silent
 
+@silent
 class AkkaSpecSpec extends WordSpec with Matchers {
 
   "An AkkaSpec" must {
diff --git a/akka-testkit/src/test/scala/akka/testkit/Coroner.scala b/akka-testkit/src/test/scala/akka/testkit/Coroner.scala
index 5ddd2dd9c4..b4fa7d05e4 100644
--- a/akka-testkit/src/test/scala/akka/testkit/Coroner.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/Coroner.scala
@@ -143,9 +143,8 @@ object Coroner {
                 #Heap usage: ${memMx.getHeapMemoryUsage()}
                 #Non-heap usage: ${memMx.getNonHeapMemoryUsage()}""".stripMargin('#'))
 
-    def dumpAllThreads: Seq[ThreadInfo] = {
-      threadMx.dumpAllThreads(threadMx.isObjectMonitorUsageSupported, threadMx.isSynchronizerUsageSupported)
-    }
+    def dumpAllThreads: Seq[ThreadInfo] =
+      threadMx.dumpAllThreads(threadMx.isObjectMonitorUsageSupported, threadMx.isSynchronizerUsageSupported).toSeq
 
     def findDeadlockedThreads: (Seq[ThreadInfo], String) = {
       val (ids, desc) = if (threadMx.isSynchronizerUsageSupported()) {
@@ -157,7 +156,7 @@ object Coroner {
         (Seq.empty, desc)
       } else {
         val maxTraceDepth = 1000 // Seems deep enough
-        (threadMx.getThreadInfo(ids, maxTraceDepth), desc)
+        (threadMx.getThreadInfo(ids, maxTraceDepth).toSeq, desc)
       }
     }
 
diff --git a/akka-testkit/src/test/scala/akka/testkit/JavaTestKitSpec.scala b/akka-testkit/src/test/scala/akka/testkit/JavaTestKitSpec.scala
index 086b43e8c2..428fb61410 100644
--- a/akka-testkit/src/test/scala/akka/testkit/JavaTestKitSpec.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/JavaTestKitSpec.scala
@@ -5,10 +5,12 @@
 package akka.testkit
 
 import language.postfixOps
-
 import akka.actor._
+import com.github.ghik.silencer.silent
+
 import scala.concurrent.duration._
 
+@silent
 class JavaTestKitSpec extends AkkaSpec with DefaultTimeout {
 
   "JavaTestKit" must {
diff --git a/akka-testkit/src/test/scala/akka/testkit/TestFSMRefSpec.scala b/akka-testkit/src/test/scala/akka/testkit/TestFSMRefSpec.scala
index e6ede5fa3f..cb8d797c18 100644
--- a/akka-testkit/src/test/scala/akka/testkit/TestFSMRefSpec.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/TestFSMRefSpec.scala
@@ -45,7 +45,7 @@ class TestFSMRefSpec extends AkkaSpec {
       val fsm = TestFSMRef(new Actor with FSM[Int, Null] {
         startWith(1, null)
         when(1) {
-          case x => stay
+          case _ => stay
         }
       }, "test-fsm-ref-2")
       fsm.isTimerActive("test") should ===(false)
@@ -65,7 +65,7 @@ class TestFSMRefSpec extends AkkaSpec {
     class TestFSMActor extends Actor with FSM[Int, Null] {
       startWith(1, null)
       when(1) {
-        case x => stay
+        case _ => stay
       }
       val supervisor = context.parent
       val name = context.self.path.name
diff --git a/akka-testkit/src/test/scala/akka/testkit/metrics/MemoryUsageSnapshotting.scala b/akka-testkit/src/test/scala/akka/testkit/metrics/MemoryUsageSnapshotting.scala
index 1e545e7ee1..08bbd9ef1f 100644
--- a/akka-testkit/src/test/scala/akka/testkit/metrics/MemoryUsageSnapshotting.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/metrics/MemoryUsageSnapshotting.scala
@@ -41,7 +41,7 @@ private[akka] trait MemoryUsageSnapshotting extends MetricsPrefix {
       metrics.get(key("non-heap-usage")).asInstanceOf[RatioGauge].getValue)
   }
 
-  private def key(k: String) = prefix + "." + k
+  private def key(k: String) = prefix.toString + "." + k
 
 }
 
diff --git a/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKit.scala b/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKit.scala
index 2f0d4e00b0..99a8a0ce0f 100644
--- a/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKit.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKit.scala
@@ -151,7 +151,7 @@ private[akka] trait MetricsKit extends MetricsKitOps {
     import collection.JavaConverters._
     registry.getMetrics.asScala.find(_._1 == key).map(_._2) match {
       case Some(existing: M) => existing
-      case Some(existing) =>
+      case Some(_) =>
         throw new IllegalArgumentException(
           "Key: [%s] is already for different kind of metric! Was [%s], expected [%s]"
             .format(key, metric.getClass.getSimpleName, tag.runtimeClass.getSimpleName))
diff --git a/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKitSpec.scala b/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKitSpec.scala
index e663895bef..22ddc19610 100644
--- a/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKitSpec.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/metrics/MetricsKitSpec.scala
@@ -53,7 +53,7 @@ class MetricsKitSpec extends WordSpec with Matchers with BeforeAndAfter with Bef
       val hist = hdrHistogram(KitKey / "hist", highestTrackableValue = maxMillis, 4, "ns")
 
       for {
-        n <- 1 to 11
+        _ <- 1 to 11
         i <- 0L to 1579331
       } hist.update(i)
 
diff --git a/akka-testkit/src/test/scala/akka/testkit/metrics/reporter/AkkaConsoleReporter.scala b/akka-testkit/src/test/scala/akka/testkit/metrics/reporter/AkkaConsoleReporter.scala
index ef43099e9a..55c8d4c2c8 100644
--- a/akka-testkit/src/test/scala/akka/testkit/metrics/reporter/AkkaConsoleReporter.scala
+++ b/akka-testkit/src/test/scala/akka/testkit/metrics/reporter/AkkaConsoleReporter.scala
@@ -9,7 +9,6 @@ import java.util
 import java.util.concurrent.TimeUnit
 import com.codahale.metrics._
 import akka.testkit.metrics._
-import scala.reflect.ClassTag
 
 /**
  * Used to report `akka.testkit.metric.Metric` types that the original `com.codahale.metrics.ConsoleReporter` is unaware of (cannot re-use directly because of private constructor).
@@ -48,9 +47,8 @@ class AkkaConsoleReporter(registry: AkkaMetricRegistry, verbose: Boolean, output
     output.flush()
   }
 
-  def printMetrics[T <: Metric](metrics: Iterable[(String, T)], printer: T => Unit)(
-      implicit clazz: ClassTag[T]): Unit = {
-    if (!metrics.isEmpty) {
+  def printMetrics[T <: Metric](metrics: Iterable[(String, T)], printer: T => Unit): Unit = {
+    if (metrics.nonEmpty) {
       printWithBanner(s"-- ${simpleName(metrics.head._2.getClass)}", '-')
       for ((key, metric) <- metrics) {
         output.println("  " + key)
diff --git a/project/AkkaDisciplinePlugin.scala b/project/AkkaDisciplinePlugin.scala
index 1e9d86eaff..c7d3ec9f53 100644
--- a/project/AkkaDisciplinePlugin.scala
+++ b/project/AkkaDisciplinePlugin.scala
@@ -33,8 +33,7 @@ object AkkaDisciplinePlugin extends AutoPlugin with ScalafixSupport {
     "akka-persistence-tck",
     "akka-remote",
     "akka-stream-tests",
-    "akka-stream-tests-tck",
-    "akka-testkit")
+    "akka-stream-tests-tck")
 
   val strictProjects = Set("akka-discovery", "akka-protobuf", "akka-coordination")