diff --git a/DesignPatternsSolution/Execise.Tests/UnitTests.cs b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
index 0a3b80e..ff4252b 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
+            var library1 = Library.getInstance();
+            var library2 = Library.getInstance();
+            Assert.AreEqual(library1, library2);
         }
 
         //test that an book was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void BookShouldRegister()
         {
+            var book = new Book("J.D. Salinger", "The Catcher in the Rye", 1951, 13);
+            var bookId = RegistrationRepository.Register(book);
+            Assert.IsFalse(bookId == -1);
         }
 
         //test that an customer was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void CustomerShouldRegister()
         {
+            var customer = new Customer("Jason Wood", "386 Broadway");
+            var customerId = RegistrationRepository.Register(customer);
+            Assert.IsFalse(customerId == -1);
         }
 
         //test that a book can be borrowed
@@ -32,7 +41,11 @@ 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.
-            
+            const int bookAmount = 13;
+            var book = new Book("J.D. Salinger", "The Catcher in the Rye", 1951, bookAmount);
+            var bookBorrowable = new BookBorrowable(book, book.Author, book.NameOrTitle, book.YearCreated, book.AvailableAmount);
+            bookBorrowable.BorrowOne();
+            Assert.IsTrue(bookBorrowable._book.AvailableAmount == bookAmount - 1);
         }       
     }
 }
diff --git a/DesignPatternsSolution/Exercise/BookBorrowable.cs b/DesignPatternsSolution/Exercise/BookBorrowable.cs
index 21bd9cf..01ff016 100644
--- a/DesignPatternsSolution/Exercise/BookBorrowable.cs
+++ b/DesignPatternsSolution/Exercise/BookBorrowable.cs
@@ -1,7 +1,24 @@
 namespace Exercise
 {
-    public class BookBorrowable 
+    public class BookBorrowable : Book
     {
-       
+        public Book _book { get; private set; }
+
+        public BookBorrowable(Book book, string author, string title, int year, int amount) : base(author, title, year, amount)
+        {
+            _book = book;
+        }
+
+        public void BorrowOne()
+        {
+            if (_book.AvailableAmount > 0)
+            {
+                _book.AvailableAmount--;
+            }
+            else
+            {
+                _book.AvailableAmount = -1;
+            }
+        }
     }
 }
diff --git a/DesignPatternsSolution/Exercise/LibObject.cs b/DesignPatternsSolution/Exercise/LibObject.cs
index cf1e2bb..3c13600 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 = AvailableAmount,
+                Id = ObjectId,
+                Info = NameOrTitle
+            };
+        }
     }
 
     public enum ObjectType
diff --git a/DesignPatternsSolution/Exercise/Library.cs b/DesignPatternsSolution/Exercise/Library.cs
index 1d9dde4..67ee0b3 100644
--- a/DesignPatternsSolution/Exercise/Library.cs
+++ b/DesignPatternsSolution/Exercise/Library.cs
@@ -3,8 +3,14 @@
     public class Library
     {
         //implement Singleton to make sure only one library will exist
+        static Library libraryInstance = new Library();
 
-        
+        private Library() { }
+
+        public static Library getInstance()
+        {
+            return libraryInstance;
+        }
 
         //Implement Register method by utilizing RegistrationRepository (complete missing parts)
         public int Register()