diff --git a/DesignPatternsSolution/Execise.Tests/UnitTests.cs b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
index 0a3b80e..4134eb9 100644
--- a/DesignPatternsSolution/Execise.Tests/UnitTests.cs
+++ b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
@@ -3,36 +3,42 @@
 
 namespace Execise.Tests
 {
-    [TestClass]
-    public class UnitTests
-    {
-        //test the two calls to library instance return same instance
-        [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
-        }
+	[TestClass]
+	public class UnitTests
+	{
+		//test the two calls to library instance return same instance
+		[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
+			Assert.AreEqual(Library.Instance, Library.Instance);
+		}
 
-        //test that an book was registered successfully by checking the returned Id value is not -1
-        [TestMethod]
-        public void BookShouldRegister()
-        {
-        }
+		//test that an book was registered successfully by checking the returned Id value is not -1
+		[TestMethod]
+		public void BookShouldRegister()
+		{
+			BookBorrowable book = new BookBorrowable(new Book("test", "test", 2017, 2), new RegisteredObject());
+			Library.Instance.Register(book);
+			Assert.IsTrue(book.GetRegistrationInfo().Id > -1);
+		}
 
-        //test that an customer was registered successfully by checking the returned Id value is not -1
-        [TestMethod]
-        public void CustomerShouldRegister()
-        {
-        }
+		//test that an customer was registered successfully by checking the returned Id value is not -1
+		[TestMethod]
+		public void CustomerShouldRegister()
+		{
+			//The assignment didnt state that we needed to create a CustomerRegisterable class?
+		}
 
-        //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.
-            
-        }       
-    }
+		//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.
+
+			//The assignment did not state that we should create a BorrowOne method in the BookBorrowable class?
+		}
+	}
 }
diff --git a/DesignPatternsSolution/Exercise/BookBorrowable.cs b/DesignPatternsSolution/Exercise/BookBorrowable.cs
index 21bd9cf..f60c8ab 100644
--- a/DesignPatternsSolution/Exercise/BookBorrowable.cs
+++ b/DesignPatternsSolution/Exercise/BookBorrowable.cs
@@ -1,7 +1,21 @@
 namespace Exercise
 {
-    public class BookBorrowable 
-    {
-       
-    }
+	public class BookBorrowable : Book, IRegistarable
+	{
+		private Book book;
+		private RegisteredObject registerable;
+
+		public BookBorrowable(Book book, RegisteredObject registerable)
+			: base(book.Author, book.NameOrTitle, book.YearCreated, book.AvailableAmount)
+		{
+			this.book = book;
+			this.registerable = registerable;
+			this.registerable.AvailableAmount = this.book.AvailableAmount;
+		}
+
+		public RegisteredObject GetRegistrationInfo()
+		{
+			return registerable;
+		}
+	}
 }
diff --git a/DesignPatternsSolution/Exercise/Library.cs b/DesignPatternsSolution/Exercise/Library.cs
index 1d9dde4..0d9bc8c 100644
--- a/DesignPatternsSolution/Exercise/Library.cs
+++ b/DesignPatternsSolution/Exercise/Library.cs
@@ -1,18 +1,26 @@
 namespace Exercise
 {
-    public class Library
-    {
-        //implement Singleton to make sure only one library will exist
+	public class Library
+	{
+		//implement Singleton to make sure only one library will exist
+		private static Library library = new Library();
 
-        
+		public static Library Instance
+		{
+			get
+			{
+				return library;
+			}
+		}
 
-        //Implement Register method by utilizing RegistrationRepository (complete missing parts)
-        public int Register()
-        {
-            // return RegistrationRepository.Register();
+		private Library()
+		{
+		}
 
-            //dummy, just to compile
-            return 0;
-        }
-    }
+		//Implement Register method by utilizing RegistrationRepository (complete missing parts)
+		public int Register(IRegistarable item)
+		{
+			return RegistrationRepository.Register(item);
+		}
+	}
 }