diff --git a/DesignPatternsSolution/Execise.Tests/UnitTests.cs b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
index 0a3b80e..2ca60bc 100644
--- a/DesignPatternsSolution/Execise.Tests/UnitTests.cs
+++ b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
@@ -12,18 +12,27 @@ public void LibraryShouldBeSingleton()
         {
             //check that when you create a Library instance second time, 
             //you get exactly the same instance as for a very first time
+            Library lib1 = Library.GetLibrary();
+            Library lib2 = Library.GetLibrary();
+            Assert.AreSame(lib1, lib2);
         }
 
         //test that an book was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void BookShouldRegister()
         {
+            Library lib = Library.GetLibrary();
+            Book book = new Book("author", "title", 2017, 10);
+            Assert.AreNotEqual(lib.Register(book), -1);
         }
 
         //test that an customer was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void CustomerShouldRegister()
         {
+            Library lib = Library.GetLibrary();
+            Customer customer = new Customer("name", "addr");
+            Assert.AreNotEqual(lib.Register(customer), -1);
         }
 
         //test that a book can be borrowed
@@ -32,7 +41,12 @@ public void CanBorrowBook()
         {
             //create a borrowable book with available amount more than one. 
             //Run BorrowOne method of the BookBorrowable instance. Check that total amount was reduced by one.
+            Book book = new Book("author", "title", 2017, 10);
+            int old = book.AvailableAmount;
+
+            BookBorrowable bookBorrowable = new BookBorrowable(null, new BorrowOne(book));
             
+            Assert.AreEqual(old - 1, book.AvailableAmount);
         }       
     }
 }
diff --git a/DesignPatternsSolution/Exercise/BookBorrowable.cs b/DesignPatternsSolution/Exercise/BookBorrowable.cs
index 21bd9cf..ef6f92c 100644
--- a/DesignPatternsSolution/Exercise/BookBorrowable.cs
+++ b/DesignPatternsSolution/Exercise/BookBorrowable.cs
@@ -1,7 +1,38 @@
 namespace Exercise
 {
-    public class BookBorrowable 
+    public abstract class ABookBorrowable
     {
-       
+        public virtual void BorrowOne() { }
+        protected BorrowOne BorrowOneProcedure;
+
+        public ABookBorrowable(BorrowOne borrowOneProcedure)
+        {
+            BorrowOneProcedure = borrowOneProcedure;
+        }
+    }
+
+    public class BookBorrowable : ABookBorrowable
+    {
+        private ABookBorrowable _bookBorrowable;
+
+        public BookBorrowable(ABookBorrowable bookBorrowable, BorrowOne borrowOne) : base(borrowOne)
+        {
+            _bookBorrowable = bookBorrowable;
+        }
+
+        public override void BorrowOne()
+        {
+            _bookBorrowable.BorrowOne();
+        }
+    }
+
+    public class BorrowOne
+    {
+        private LibObject item;
+
+        public BorrowOne(LibObject item)
+        {
+            item.AvailableAmount--;
+        }
     }
 }
diff --git a/DesignPatternsSolution/Exercise/LibObject.cs b/DesignPatternsSolution/Exercise/LibObject.cs
index cf1e2bb..8fc5465 100644
--- a/DesignPatternsSolution/Exercise/LibObject.cs
+++ b/DesignPatternsSolution/Exercise/LibObject.cs
@@ -1,12 +1,16 @@
 namespace Exercise
 {
-    public abstract class LibObject
+    public abstract class LibObject:IRegistarable
     {
         public int ObjectId { get; set; }
         public int AvailableAmount { get; set; }
         public string NameOrTitle { get; set; }
         public ObjectType ObjType { get; set; }
         public int YearCreated { get; set; }
+        public RegisteredObject GetRegistrationInfo()
+        {
+            return new RegisteredObject();
+        }
     }
 
     public enum ObjectType
diff --git a/DesignPatternsSolution/Exercise/Library.cs b/DesignPatternsSolution/Exercise/Library.cs
index 1d9dde4..d9b00fa 100644
--- a/DesignPatternsSolution/Exercise/Library.cs
+++ b/DesignPatternsSolution/Exercise/Library.cs
@@ -3,16 +3,22 @@
     public class Library
     {
         //implement Singleton to make sure only one library will exist
-
+        private static Library instance = new Library();
         
+        private Library() { }
+
+        public static Library GetLibrary()
+        {
+            return instance;
+        }
 
         //Implement Register method by utilizing RegistrationRepository (complete missing parts)
-        public int Register()
+        public int Register(IRegistarable item)
         {
             // return RegistrationRepository.Register();
 
             //dummy, just to compile
-            return 0;
+            return RegistrationRepository.Register(item);
         }
     }
 }