diff --git a/src/core/Akka.Streams.TestKit/ChainSetup.cs b/src/core/Akka.Streams.TestKit/ChainSetup.cs
index ec5b931eb0d..d83bb797228 100644
--- a/src/core/Akka.Streams.TestKit/ChainSetup.cs
+++ b/src/core/Akka.Streams.TestKit/ChainSetup.cs
@@ -6,6 +6,7 @@
 //-----------------------------------------------------------------------
 
 using System;
+using System.Threading.Tasks;
 using Akka.Actor;
 using Akka.Streams.Dsl;
 using Akka.TestKit;
@@ -15,6 +16,9 @@ namespace Akka.Streams.TestKit
 {
     public class ChainSetup<TIn, TOut, TMat>
     {
+        private readonly Func<Source<TOut, NotUsed>, ActorMaterializer, IPublisher<TOut>> _toPublisher;
+        private readonly Func<Flow<TIn, TIn, NotUsed>, Flow<TIn, TOut, TMat>> _stream;
+        private readonly ActorMaterializer _materializer;
         protected readonly TestKitBase System;
 
         public ChainSetup(
@@ -24,18 +28,11 @@ public ChainSetup(
             Func<Source<TOut, NotUsed>, ActorMaterializer, IPublisher<TOut>> toPublisher,
             TestKitBase system)
         {
-
             Settings = settings;
             System = system;
-
-            Upstream = system.CreateManualPublisherProbe<TIn>();
-            Downstream = system.CreateSubscriberProbe<TOut>();
-
-            var s = Source.FromPublisher(Upstream).Via(stream(Flow.Identity<TIn>().Select(x => x).Named("buh")));
-            Publisher = toPublisher(s, materializer);
-            UpstreamSubscription = Upstream.ExpectSubscription();
-            Publisher.Subscribe(Downstream);
-            DownstreamSubscription = Downstream.ExpectSubscription();
+            _toPublisher = toPublisher;
+            _stream = stream;
+            _materializer = materializer;
         }
 
         public ChainSetup(
@@ -57,11 +54,87 @@ public ChainSetup(
         {
         }
 
+        [Obsolete("Will be removed after async_testkit conversion is complete. Use InitializeAsync instead")]
+        public ChainSetup<TIn, TOut, TMat> Initialize()
+            => InitializeAsync()
+                .ConfigureAwait(false).GetAwaiter().GetResult();
+        
+        public virtual async Task<ChainSetup<TIn, TOut, TMat>> InitializeAsync()
+        {
+            _upstream = System.CreateManualPublisherProbe<TIn>();
+            _downstream = System.CreateSubscriberProbe<TOut>();
+
+            var s = Source.FromPublisher(_upstream).Via(_stream(Flow.Identity<TIn>().Select(x => x).Named("buh")));
+            _publisher = _toPublisher(s, _materializer);
+            _upstreamSubscription = await _upstream.ExpectSubscriptionAsync();
+            _publisher.Subscribe(_downstream);
+            _downstreamSubscription = await _downstream.ExpectSubscriptionAsync();
+
+            Initialized = true;
+            
+            return this;
+        }
+
+        private TestPublisher.ManualProbe<TIn> _upstream;
+        private TestSubscriber.ManualProbe<TOut> _downstream;
+        private IPublisher<TOut> _publisher;
+        private StreamTestKit.PublisherProbeSubscription<TIn> _upstreamSubscription;
+        private ISubscription _downstreamSubscription;
+
+        public bool Initialized { get; private set; }
+
         public ActorMaterializerSettings Settings { get; }
-        public TestPublisher.ManualProbe<TIn> Upstream { get; }
-        public TestSubscriber.ManualProbe<TOut> Downstream { get; }
-        public IPublisher<TOut> Publisher { get; }
-        public StreamTestKit.PublisherProbeSubscription<TIn> UpstreamSubscription { get; }
-        public ISubscription DownstreamSubscription { get; }
+
+        public TestPublisher.ManualProbe<TIn> Upstream
+        {
+            get
+            {
+                EnsureInitialized();
+                return _upstream;
+            }
+        }
+
+        public TestSubscriber.ManualProbe<TOut> Downstream
+        {
+            get
+            {
+                EnsureInitialized();
+                return _downstream;
+            }
+        }
+
+        public IPublisher<TOut> Publisher
+        {
+            get
+            {
+                EnsureInitialized();
+                return _publisher;
+            }
+        }
+
+        public StreamTestKit.PublisherProbeSubscription<TIn> UpstreamSubscription
+        {
+            get
+            {
+                EnsureInitialized();
+                return _upstreamSubscription;
+            }
+        }
+
+        public ISubscription DownstreamSubscription
+        {
+            get
+            {
+                EnsureInitialized();
+                return _downstreamSubscription;
+            }
+        }
+
+        protected virtual void EnsureInitialized()
+        {
+            if (!Initialized)
+                throw new InvalidOperationException(
+                    $"ChainSetup has not been initialized. Please make sure to call {nameof(InitializeAsync)} first.");
+        }
     }
 }
diff --git a/src/core/Akka.Streams.TestKit/ScriptedTest.cs b/src/core/Akka.Streams.TestKit/ScriptedTest.cs
index f402f9c228e..9919f6ff0a2 100644
--- a/src/core/Akka.Streams.TestKit/ScriptedTest.cs
+++ b/src/core/Akka.Streams.TestKit/ScriptedTest.cs
@@ -15,6 +15,7 @@
 using Akka.Streams.Dsl;
 using Akka.TestKit;
 using Akka.Util;
+using Akka.Util.Internal;
 using Reactive.Streams;
 using Xunit.Abstractions;
 
@@ -306,7 +307,8 @@ protected void RunScript<TIn2, TOut2, TMat2>(Script<TIn2, TOut2> script, ActorMa
             Func<Flow<TIn2, TIn2, NotUsed>, Flow<TIn2, TOut2, TMat2>> op,
             int maximumOverrun = 3, int maximumRequest = 3, int maximumBuffer = 3)
         {
-            new ScriptRunner<TIn2, TOut2, TMat2>(op, settings, script, maximumOverrun, maximumRequest, maximumBuffer, this).Run();
+            new ScriptRunner<TIn2, TOut2, TMat2>(op, settings, script, maximumOverrun, maximumRequest, maximumBuffer, this)
+                .Initialize().AsInstanceOf<ScriptRunner<TIn2, TOut2, TMat2>>().Run();
         }
 
         protected static IPublisher<TOut> ToPublisher<TOut>(Source<TOut, NotUsed> source, IMaterializer materializer)
diff --git a/src/core/Akka.Streams.Tests/Dsl/FlowSpec.cs b/src/core/Akka.Streams.Tests/Dsl/FlowSpec.cs
index e95a1ff3d2b..d09d420afc9 100644
--- a/src/core/Akka.Streams.Tests/Dsl/FlowSpec.cs
+++ b/src/core/Akka.Streams.Tests/Dsl/FlowSpec.cs
@@ -63,10 +63,12 @@ public void A_flow_must_request_initial_elements_from_upstream(string name, int
 
             if (name.Equals("identity"))
                 setup = new ChainSetup<int, int, NotUsed>(Identity, Settings.WithInputBuffer(n, n),
-                    (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                    (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                    .Initialize();
             else
                 setup = new ChainSetup<int, int, NotUsed>(Identity2, Settings.WithInputBuffer(n, n),
-                    (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                    (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                    .Initialize();
 
             setup.Upstream.ExpectRequest(setup.UpstreamSubscription, setup.Settings.MaxInputBufferSize);
         }
@@ -75,7 +77,8 @@ public void A_flow_must_request_initial_elements_from_upstream(string name, int
         public void A_Flow_must_request_more_elements_from_upstream_when_downstream_requests_more_elements()
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings,
-                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                .Initialize();
             setup.Upstream.ExpectRequest(setup.UpstreamSubscription, Settings.MaxInputBufferSize);
             setup.DownstreamSubscription.Request(1);
             setup.Upstream.ExpectNoMsg(TimeSpan.FromMilliseconds(100));
@@ -96,7 +99,8 @@ public void A_Flow_must_request_more_elements_from_upstream_when_downstream_requ
         public void A_Flow_must_deliver_events_when_publisher_sends_elements_and_then_completes()
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings,
-                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                .Initialize();
             setup.DownstreamSubscription.Request(1);
             setup.UpstreamSubscription.SendNext("test");
             setup.UpstreamSubscription.SendComplete();
@@ -108,7 +112,8 @@ public void A_Flow_must_deliver_events_when_publisher_sends_elements_and_then_co
         public void A_Flow_must_deliver_complete_signal_when_publisher_immediately_completes()
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings,
-                  (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                  (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                .Initialize();
             setup.UpstreamSubscription.SendComplete();
             setup.Downstream.ExpectComplete();
         }
@@ -117,7 +122,8 @@ public void A_Flow_must_deliver_complete_signal_when_publisher_immediately_compl
         public void A_Flow_must_deliver_error_signal_when_publisher_immediately_fails()
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings,
-                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                .Initialize();
             var weirdError = new Exception("weird test exception");
             setup.UpstreamSubscription.SendError(weirdError);
             setup.Downstream.ExpectError().Should().Be(weirdError);
@@ -127,7 +133,8 @@ public void A_Flow_must_deliver_error_signal_when_publisher_immediately_fails()
         public void A_Flow_must_cancel_upstream_when_single_subscriber_cancels_subscription_while_receiving_data()
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
-                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this);
+                (settings, factory) => ActorMaterializer.Create(factory, settings), ToPublisher, this)
+                .Initialize();
             setup.DownstreamSubscription.Request(5);
             setup.UpstreamSubscription.ExpectRequest(1);
             setup.UpstreamSubscription.SendNext("test");
@@ -350,7 +357,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_adapt_speed_to_the_c
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this)
+                .Initialize();
             var downstream2 = this.CreateManualSubscriberProbe<string>();
             setup.Publisher.Subscribe(downstream2);
             var downstream2Subscription = downstream2.ExpectSubscription();
@@ -379,7 +387,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_support_slow_subscri
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 2), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 2), this)
+                .Initialize();
             var downstream2 = this.CreateManualSubscriberProbe<string>();
             setup.Publisher.Subscribe(downstream2);
             var downstream2Subscription = downstream2.ExpectSubscription();
@@ -422,7 +431,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_support_incoming_sub
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this)
+                .Initialize();
 
             setup.DownstreamSubscription.Request(5);
             setup.Upstream.ExpectRequest(setup.UpstreamSubscription, 1);
@@ -463,7 +473,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_be_unblocked_when_bl
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this)
+                .Initialize();
             var downstream2 = this.CreateManualSubscriberProbe<string>();
             setup.Publisher.Subscribe(downstream2);
             var downstream2Subscription = downstream2.ExpectSubscription();
@@ -503,7 +514,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_call_future_subscrib
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this)
+                .Initialize();
             var downstream2 = this.CreateManualSubscriberProbe<string>();
             // don't link it just yet
 
@@ -547,7 +559,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_call_future_subscrib
                 throw new TestException("test");
             }), Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 1), this)
+                .Initialize();
 
             setup.DownstreamSubscription.Request(1);
             setup.UpstreamSubscription.ExpectRequest(1);
@@ -567,7 +580,8 @@ public void A_Flow_with_multiple_subscribers_FanOutBox_must_call_future_subscrib
         {
             var setup = new ChainSetup<string, string, NotUsed>(Identity, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 16), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 16), this)
+                .Initialize();
 
             // make sure stream is initialized before canceling downstream
             Thread.Sleep(100);
@@ -596,7 +610,8 @@ public void A_broken_Flow_must_cancel_upstream_and_call_onError_on_current_and_f
         {
             var setup = new ChainSetup<string, string, NotUsed>(FaultyFlow<string,string,string>, Settings.WithInputBuffer(1, 1),
                 (settings, factory) => ActorMaterializer.Create(factory, settings),
-                (source, materializer) => ToFanoutPublisher(source, materializer, 16), this);
+                (source, materializer) => ToFanoutPublisher(source, materializer, 16), this)
+                .Initialize();
 
             Action<TestSubscriber.ManualProbe<string>> checkError = sprobe =>
             {