diff --git a/DesignPatternsSolution/Execise.Tests/UnitTests.cs b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
index 0a3b80e..fd6b341 100644
--- a/DesignPatternsSolution/Execise.Tests/UnitTests.cs
+++ b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
@@ -10,29 +10,39 @@ public class UnitTests
         [TestMethod]
         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
+            var l1 = Library.GetInstance();
+            var l2 = Library.GetInstance();
+
+            Assert.AreSame(l1, l2);
         }
 
         //test that an book was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void BookShouldRegister()
         {
+            int value = RegistrationRepository.Register(new Book("Author", "Title", 1997, 5));
+
+            Assert.AreNotEqual<int>(-1, value);
         }
 
         //test that an customer was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void CustomerShouldRegister()
         {
+            int value = RegistrationRepository.Register(new Customer("Customer Name", "Address"));
+
+            Assert.AreNotEqual<int>(-1, value);
         }
 
         //test that a book can be borrowed
         [TestMethod]
         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.
-            
+            var book = new Book("Author", "Title", 1997, 5);
+            var borrowable = new BookBorrowable(book);
+
+            borrowable.BorrowOne();
+            Assert.AreEqual<int>(4, book.AvailableAmount);
         }       
     }
 }
diff --git a/DesignPatternsSolution/Exercise/BookBorrowable.cs b/DesignPatternsSolution/Exercise/BookBorrowable.cs
index 21bd9cf..8c70b74 100644
--- a/DesignPatternsSolution/Exercise/BookBorrowable.cs
+++ b/DesignPatternsSolution/Exercise/BookBorrowable.cs
@@ -1,7 +1,24 @@
 namespace Exercise
 {
-    public class BookBorrowable 
+    public class BookBorrowable : Book
     {
-       
+       private Book Book { get; set; }
+
+        public BookBorrowable(Book bookToBorrow) : base(bookToBorrow.Author, bookToBorrow.NameOrTitle, bookToBorrow.YearCreated, bookToBorrow.YearCreated)
+        {
+            this.Book = bookToBorrow;
+        }
+
+        public bool BorrowOne()
+        {
+            if (this.Book.AvailableAmount > 0)
+            {
+                this.Book.AvailableAmount--;
+                return true;
+            }
+            else
+                return false;
+                
+        }
     }
 }
diff --git a/DesignPatternsSolution/Exercise/Item.cs b/DesignPatternsSolution/Exercise/Item.cs
index 92c21e1..475a885 100644
--- a/DesignPatternsSolution/Exercise/Item.cs
+++ b/DesignPatternsSolution/Exercise/Item.cs
@@ -1,4 +1,6 @@
-namespace Exercise
+using System;
+
+namespace Exercise
 {
     public abstract class Item : LibObject
     {
diff --git a/DesignPatternsSolution/Exercise/LibObject.cs b/DesignPatternsSolution/Exercise/LibObject.cs
index cf1e2bb..756d181 100644
--- a/DesignPatternsSolution/Exercise/LibObject.cs
+++ b/DesignPatternsSolution/Exercise/LibObject.cs
@@ -1,12 +1,22 @@
 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()
+            {
+                AvailableAmount = this.AvailableAmount,
+                Id = this.ObjectId,
+                Info = this.NameOrTitle
+            };
+        }
     }
 
     public enum ObjectType
diff --git a/DesignPatternsSolution/Exercise/Library.cs b/DesignPatternsSolution/Exercise/Library.cs
index 1d9dde4..c86c759 100644
--- a/DesignPatternsSolution/Exercise/Library.cs
+++ b/DesignPatternsSolution/Exercise/Library.cs
@@ -2,9 +2,10 @@
 {
     public class Library
     {
-        //implement Singleton to make sure only one library will exist
+        private static Library Instance { get; set; }
 
-        
+        private Library() { Instance = new Library(); }
+        public static Library GetInstance() { return Library.Instance; }
 
         //Implement Register method by utilizing RegistrationRepository (complete missing parts)
         public int Register()