diff --git a/src/TestabilityKata.Tests/TestabilityKata.Tests.csproj b/src/TestabilityKata.Tests/TestabilityKata.Tests.csproj
index f8c14f3..14ce7f0 100644
--- a/src/TestabilityKata.Tests/TestabilityKata.Tests.csproj
+++ b/src/TestabilityKata.Tests/TestabilityKata.Tests.csproj
@@ -1,17 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="FluffySpoon.Testing.Autofake.Autofac" Version="1.0.5" />
-    <PackageReference Include="FluffySpoon.Testing.Autofake.NSubstitute" Version="1.0.5" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0-preview-20170628-02" />
-    <PackageReference Include="MSTest.TestAdapter" Version="1.1.18" />
-    <PackageReference Include="MSTest.TestFramework" Version="1.1.18" />
+    <PackageReference Include="FluffySpoon.Testing.Autofake.Autofac" Version="1.34.0" />
+    <PackageReference Include="FluffySpoon.Testing.Autofake.NSubstitute" Version="1.34.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
+    <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/TestabilityKata/ICustomFileWriter.cs b/src/TestabilityKata/ICustomFileWriter.cs
new file mode 100644
index 0000000..2f2715f
--- /dev/null
+++ b/src/TestabilityKata/ICustomFileWriter.cs
@@ -0,0 +1,9 @@
+namespace TestabilityKata
+{
+    public interface ICustomFileWriter
+    {
+        string FilePath { get; }
+
+        void AppendLine(string line);
+    }
+}
\ No newline at end of file
diff --git a/src/TestabilityKata/ICustomFileWriterFactory.cs b/src/TestabilityKata/ICustomFileWriterFactory.cs
new file mode 100644
index 0000000..6c048c2
--- /dev/null
+++ b/src/TestabilityKata/ICustomFileWriterFactory.cs
@@ -0,0 +1,7 @@
+namespace TestabilityKata
+{
+    public interface ICustomFileWriterFactory
+    {
+        ICustomFileWriter Create(string filePath);
+    }
+}
\ No newline at end of file
diff --git a/src/TestabilityKata/ILogger.cs b/src/TestabilityKata/ILogger.cs
new file mode 100644
index 0000000..c2e8a99
--- /dev/null
+++ b/src/TestabilityKata/ILogger.cs
@@ -0,0 +1,7 @@
+namespace TestabilityKata
+{
+    public interface ILogger
+    {
+        void Log(LogLevel logLevel, string logText);
+    }
+}
\ No newline at end of file
diff --git a/src/TestabilityKata/IMailSender.cs b/src/TestabilityKata/IMailSender.cs
new file mode 100644
index 0000000..89209c3
--- /dev/null
+++ b/src/TestabilityKata/IMailSender.cs
@@ -0,0 +1,7 @@
+namespace TestabilityKata
+{
+    public interface IMailSender
+    {
+        void SendMail(string recipient, string content);
+    }
+}
\ No newline at end of file
diff --git a/src/TestabilityKata/IProgram.cs b/src/TestabilityKata/IProgram.cs
new file mode 100644
index 0000000..944bf3b
--- /dev/null
+++ b/src/TestabilityKata/IProgram.cs
@@ -0,0 +1,7 @@
+namespace TestabilityKata
+{
+    public interface IProgram
+    {
+        void Run();
+    }
+}
\ No newline at end of file
diff --git a/src/TestabilityKata/Program.cs b/src/TestabilityKata/Program.cs
index 88e9322..38cbb8c 100644
--- a/src/TestabilityKata/Program.cs
+++ b/src/TestabilityKata/Program.cs
@@ -3,7 +3,7 @@
 
 namespace TestabilityKata
 {
-    public class Program
+    public class Program : IProgram
     {
         public static void Main(string[] args)
         {
@@ -16,12 +16,12 @@ public static void Main(string[] args)
                 .Run();
         }
 
-        private readonly Logger logger;
-        private readonly MailSender mailSender;
+        private readonly ILogger logger;
+        private readonly IMailSender mailSender;
 
         public Program(
-            Logger logger,
-            MailSender mailSender)
+            ILogger logger,
+            IMailSender mailSender)
         {
             this.logger = logger;
             this.mailSender = mailSender;
@@ -49,14 +49,14 @@ public enum LogLevel
         Error
     }
 
-    public class Logger
+    public class Logger : ILogger
     {
-        private readonly MailSender mailSender;
-        private readonly CustomFileWriterFactory customFileWriterFactory;
+        private readonly IMailSender mailSender;
+        private readonly ICustomFileWriterFactory customFileWriterFactory;
 
         public Logger(
-            MailSender mailSender,
-            CustomFileWriterFactory customFileWriterFactory)
+            IMailSender mailSender,
+            ICustomFileWriterFactory customFileWriterFactory)
         {
             this.mailSender = mailSender;
             this.customFileWriterFactory = customFileWriterFactory;
@@ -80,7 +80,7 @@ public void Log(LogLevel logLevel, string logText)
         }
     }
 
-    public class MailSender
+    public class MailSender : IMailSender
     {
         public void SendMail(string recipient, string content)
         {
@@ -92,17 +92,17 @@ public void SendMail(string recipient, string content)
         }
     }
 
-    public class CustomFileWriterFactory
+    public class CustomFileWriterFactory : ICustomFileWriterFactory
     {
-        private readonly MailSender mailSender;
+        private readonly IMailSender mailSender;
 
         public CustomFileWriterFactory(
-            MailSender mailSender)
+            IMailSender mailSender)
         {
             this.mailSender = mailSender;
         }
 
-        public CustomFileWriter Create(string filePath)
+        public ICustomFileWriter Create(string filePath)
         {
             return new CustomFileWriter(
                 mailSender, 
@@ -110,14 +110,14 @@ public CustomFileWriter Create(string filePath)
         }
     }
 
-    public class CustomFileWriter
+    public class CustomFileWriter : ICustomFileWriter
     {
-        private readonly MailSender mailSender;
+        private readonly IMailSender mailSender;
 
         public string FilePath { get; }
 
         public CustomFileWriter(
-            MailSender mailSender,
+            IMailSender mailSender,
             string filePath)
         {
             this.mailSender = mailSender;
diff --git a/src/TestabilityKata/TestabilityKata.csproj b/src/TestabilityKata/TestabilityKata.csproj
index ce1697a..41f1d5a 100644
--- a/src/TestabilityKata/TestabilityKata.csproj
+++ b/src/TestabilityKata/TestabilityKata.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
   </PropertyGroup>
 
 </Project>