diff --git a/LightweightIocContainer/Interfaces/IIocContainer.cs b/LightweightIocContainer/Interfaces/IIocContainer.cs
index 79e4746..0b5d2bd 100644
--- a/LightweightIocContainer/Interfaces/IIocContainer.cs
+++ b/LightweightIocContainer/Interfaces/IIocContainer.cs
@@ -59,6 +59,7 @@ namespace LightweightIocContainer.Interfaces
         /// <typeparam name="TInterface">The Interface to register</typeparam>
         /// <param name="unitTestCallback">The <see cref="ResolveCallback{T}"/> for the callback</param>
         /// <returns>The created <see cref="IRegistration"/></returns>
+        [Obsolete("RegisterUnitTestCallback is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
         IUnitTestCallbackRegistration<TInterface> RegisterUnitTestCallback<TInterface>(ResolveCallback<TInterface> unitTestCallback);
 
         /// <summary>
diff --git a/LightweightIocContainer/Interfaces/Registrations/IUnitTestCallbackRegistration.cs b/LightweightIocContainer/Interfaces/Registrations/IUnitTestCallbackRegistration.cs
index 2dd0123..d10f74e 100644
--- a/LightweightIocContainer/Interfaces/Registrations/IUnitTestCallbackRegistration.cs
+++ b/LightweightIocContainer/Interfaces/Registrations/IUnitTestCallbackRegistration.cs
@@ -2,17 +2,21 @@
 // Created: 2019-10-15
 // Copyright(c) 2019 SimonG. All Rights Reserved.
 
+using System;
+
 namespace LightweightIocContainer.Interfaces.Registrations
 {
     /// <summary>
     /// A special <see cref="IRegistration"/> that allows to set a <see cref="ResolveCallback{T}"/> as a callback that is called on <see cref="IIocContainer.Resolve{T}()"/>
     /// </summary>
     /// <typeparam name="TInterface"></typeparam>
+    [Obsolete("IUnitTestCallbackRegistration is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
     public interface IUnitTestCallbackRegistration<out TInterface> : IRegistration
     {
         /// <summary>
         /// An <see cref="ResolveCallback{T}"/> that is set as a callback that is called on <see cref="IIocContainer.Resolve{T}()"/>
         /// </summary>
+        [Obsolete("UnitTestResolveCallback is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
         ResolveCallback<TInterface> UnitTestResolveCallback { get; }
     }
 }
\ No newline at end of file
diff --git a/LightweightIocContainer/IocContainer.cs b/LightweightIocContainer/IocContainer.cs
index 14f01af..8096bf9 100644
--- a/LightweightIocContainer/IocContainer.cs
+++ b/LightweightIocContainer/IocContainer.cs
@@ -115,6 +115,7 @@ namespace LightweightIocContainer
         /// <typeparam name="TInterface">The Interface to register</typeparam>
         /// <param name="unitTestCallback">The <see cref="ResolveCallback{T}"/> for the callback</param>
         /// <returns>The created <see cref="IRegistration"/></returns>
+        [Obsolete("RegisterUnitTestCallback is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
         public IUnitTestCallbackRegistration<TInterface> RegisterUnitTestCallback<TInterface>(ResolveCallback<TInterface> unitTestCallback)
         {
             IUnitTestCallbackRegistration<TInterface> registration = _registrationFactory.RegisterUnitTestCallback(unitTestCallback);
@@ -209,10 +210,13 @@ namespace LightweightIocContainer
 
             T resolvedInstance;
 
+            //TODO: remove this #pragma when IUnitTestCallbackRegistration is removed
+#pragma warning disable 618
             if (registration is IUnitTestCallbackRegistration<T> unitTestCallbackRegistration)
             {
                 resolvedInstance = unitTestCallbackRegistration.UnitTestResolveCallback.Invoke(arguments);
             }
+#pragma warning restore 618
             else if (registration is IRegistrationBase<T> defaultRegistration)
             {
                 if (defaultRegistration.Lifestyle == Lifestyle.Singleton)
diff --git a/LightweightIocContainer/Registrations/RegistrationFactory.cs b/LightweightIocContainer/Registrations/RegistrationFactory.cs
index 41ec968..d780413 100644
--- a/LightweightIocContainer/Registrations/RegistrationFactory.cs
+++ b/LightweightIocContainer/Registrations/RegistrationFactory.cs
@@ -66,6 +66,7 @@ namespace LightweightIocContainer.Registrations
             return new TypedFactoryRegistration<TFactory>(typeof(TFactory), _iocContainer);
         }
 
+        [Obsolete("RegisterUnitTestCallback is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
         public IUnitTestCallbackRegistration<TInterface> RegisterUnitTestCallback<TInterface>(ResolveCallback<TInterface> unitTestResolveCallback)
         {
             return new UnitTestCallbackRegistration<TInterface>(typeof(TInterface), unitTestResolveCallback);
diff --git a/LightweightIocContainer/Registrations/UnitTestCallbackRegistration.cs b/LightweightIocContainer/Registrations/UnitTestCallbackRegistration.cs
index 529d1e5..c489510 100644
--- a/LightweightIocContainer/Registrations/UnitTestCallbackRegistration.cs
+++ b/LightweightIocContainer/Registrations/UnitTestCallbackRegistration.cs
@@ -12,6 +12,7 @@ namespace LightweightIocContainer.Registrations
     /// A special <see cref="IRegistration"/> that allows to set a <see cref="ResolveCallback{T}"/> as a callback that is called on <see cref="IIocContainer.Resolve{T}()"/>
     /// </summary>
     /// <typeparam name="TInterface"></typeparam>
+    [Obsolete("UnitTestCallbackRegistration is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
     public class UnitTestCallbackRegistration<TInterface> : IUnitTestCallbackRegistration<TInterface>
     {
         /// <summary>
diff --git a/Test.LightweightIocContainer/IocContainerTest.cs b/Test.LightweightIocContainer/IocContainerTest.cs
index ccffa6c..39b1add 100644
--- a/Test.LightweightIocContainer/IocContainerTest.cs
+++ b/Test.LightweightIocContainer/IocContainerTest.cs
@@ -1,3 +1,4 @@
+using System;
 using JetBrains.Annotations;
 using LightweightIocContainer;
 using LightweightIocContainer.Exceptions;
@@ -179,6 +180,7 @@ namespace Test.LightweightIocContainer
         }
 
         [Test]
+        [Obsolete("RegisterUnitTestCallback is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
         public void TestRegisterUnitTestCallback()
         {
             Assert.DoesNotThrow(() => _iocContainer.RegisterUnitTestCallback<ITest>(delegate {return new Test(); }));
@@ -436,6 +438,7 @@ namespace Test.LightweightIocContainer
         }
 
         [Test]
+        [Obsolete("RegisterUnitTestCallback is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
         public void TestResolveUnitTestCallbackRegistration()
         {
             ITest callbackTest = new Test();
diff --git a/Test.LightweightIocContainer/UnitTestCallbackRegistrationTest.cs b/Test.LightweightIocContainer/UnitTestCallbackRegistrationTest.cs
index 0e4a099..f9392db 100644
--- a/Test.LightweightIocContainer/UnitTestCallbackRegistrationTest.cs
+++ b/Test.LightweightIocContainer/UnitTestCallbackRegistrationTest.cs
@@ -2,6 +2,7 @@
 // Created: 2019-10-15
 // Copyright(c) 2019 SimonG. All Rights Reserved.
 
+using System;
 using LightweightIocContainer;
 using LightweightIocContainer.Interfaces;
 using LightweightIocContainer.Interfaces.Registrations;
@@ -12,6 +13,7 @@ using NUnit.Framework;
 namespace Test.LightweightIocContainer
 {
     [TestFixture]
+    [Obsolete("UnitTestCallbackRegistration is deprecated, use `WithFactoryMethod()` from ISingleTypeRegistration instead.")]
     public class UnitTestCallbackRegistrationTest
     {
         private interface ITest