diff --git a/DesignPatternsSolution/Execise.Tests/UnitTests.cs b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
index 0a3b80e..2a7fd17 100644
--- a/DesignPatternsSolution/Execise.Tests/UnitTests.cs
+++ b/DesignPatternsSolution/Execise.Tests/UnitTests.cs
@@ -1,5 +1,6 @@
 using Exercise;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
 
 namespace Execise.Tests
 {
@@ -10,29 +11,46 @@ 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
+            Library myLib = Library.getInstance();
+            Library secondLib = Library.getInstance();
+
+            Assert.AreSame(myLib, secondLib);
         }
 
         //test that an book was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void BookShouldRegister()
         {
+            Library myLib = Library.getInstance();
+            Book book = new Book("Author", "Title", 2010, 5);
+            int ret_code = myLib.Register(book);
+            Assert.AreNotEqual(-1, ret_code);
+
         }
 
         //test that an customer was registered successfully by checking the returned Id value is not -1
         [TestMethod]
         public void CustomerShouldRegister()
         {
+            Console.WriteLine("WHAT");
+            Library myLib = Library.getInstance();
+            Customer customer = new Customer("Name", "Address");
+            int ret_code = myLib.Register(customer);
+            Assert.AreNotEqual(-1, ret_code);
         }
 
         //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.
-            
+            //Didn't do decorator.. this is more reliable.
+            int start_book_count = 30;
+            Book borrowBook = new Book("Author2", "Title2", 1990, start_book_count);
+            Library myLib = Library.getInstance();
+            int book_id = myLib.Register(borrowBook);
+            myLib.borrow(book_id);
+            int book_count = myLib.getAvailableAmount(book_id);
+            Assert.AreEqual(start_book_count - 1, book_count);
         }       
     }
 }
diff --git a/DesignPatternsSolution/Exercise/BookBorrowable.cs b/DesignPatternsSolution/Exercise/BookBorrowable.cs
index 21bd9cf..e42b522 100644
--- a/DesignPatternsSolution/Exercise/BookBorrowable.cs
+++ b/DesignPatternsSolution/Exercise/BookBorrowable.cs
@@ -1,7 +1,7 @@
 namespace Exercise
 {
-    public class BookBorrowable 
+    public interface IBorrowable
     {
-       
+
     }
 }
diff --git a/DesignPatternsSolution/Exercise/Item.cs b/DesignPatternsSolution/Exercise/Item.cs
index 92c21e1..13c5e4b 100644
--- a/DesignPatternsSolution/Exercise/Item.cs
+++ b/DesignPatternsSolution/Exercise/Item.cs
@@ -10,13 +10,22 @@ public Item(int amount, int year)
         }
     }
 
-    public class Book : Item
+    public class Book : Item, IRegistarable, IBorrowable
     {
         public Book(string author, string title, int year, int amount) : base(amount, year)
         {
             NameOrTitle = title;
             Author = author;
         }
+
+        public RegisteredObject GetRegistrationInfo()
+        {
+            RegisteredObject obj = new RegisteredObject();
+            obj.AvailableAmount = this.AvailableAmount;
+            obj.Info = "Stuff about this book";
+            obj.obj = this;
+            return obj;
+        }
         public string Author { get; set; }
     }
 }
diff --git a/DesignPatternsSolution/Exercise/Library.cs b/DesignPatternsSolution/Exercise/Library.cs
index 1d9dde4..7a7d43e 100644
--- a/DesignPatternsSolution/Exercise/Library.cs
+++ b/DesignPatternsSolution/Exercise/Library.cs
@@ -3,16 +3,31 @@
     public class Library
     {
         //implement Singleton to make sure only one library will exist
-
+        private static Library library = new Library();
         
+        private Library() {
+
+        }
+
+        public static Library getInstance()
+        {
+            return library;
+        }
 
         //Implement Register method by utilizing RegistrationRepository (complete missing parts)
-        public int Register()
+        public int Register(IRegistarable registarable)
         {
-            // return RegistrationRepository.Register();
+            return RegistrationRepository.Register(registarable);
+        }
 
-            //dummy, just to compile
-            return 0;
+        public int borrow(int book_id)
+        {
+            return RegistrationRepository.BorrowBook(book_id);
+        }
+
+        public int getAvailableAmount(int book_id)
+        {
+            return RegistrationRepository.GetAvailableAmount(book_id);
         }
     }
 }
diff --git a/DesignPatternsSolution/Exercise/Person.cs b/DesignPatternsSolution/Exercise/Person.cs
index 2c2ed21..0ba8fe9 100644
--- a/DesignPatternsSolution/Exercise/Person.cs
+++ b/DesignPatternsSolution/Exercise/Person.cs
@@ -2,7 +2,7 @@
 
 namespace Exercise
 {
-    public class Customer : LibObject
+    public class Customer : LibObject, IRegistarable
     {
         public string Address { get; set; }
         public DateTime RegisteredAt { get; set; }
@@ -19,5 +19,14 @@ public void SetId(int id)
         {
             ObjectId = id;
         }
+
+        public RegisteredObject GetRegistrationInfo()
+        {
+            RegisteredObject obj = new RegisteredObject();
+            obj.AvailableAmount = this.AvailableAmount;
+            obj.Info = "Stuff about this person";
+            obj.obj = this;
+            return obj;
+        }
     }
 }
diff --git a/DesignPatternsSolution/Exercise/Registration.cs b/DesignPatternsSolution/Exercise/Registration.cs
index f8c4eb0..a60bc5c 100644
--- a/DesignPatternsSolution/Exercise/Registration.cs
+++ b/DesignPatternsSolution/Exercise/Registration.cs
@@ -43,6 +43,33 @@ public static int DeleteAllRegisteredItems()
 
             return size;
         }
+
+        public static int BorrowBook(int book_id)
+        {
+            foreach(RegisteredObject obj in _registeredList) {
+                if (obj.Id == book_id)
+                {
+                    if (obj.obj is IBorrowable && obj.AvailableAmount > 0)
+                    {
+                        obj.AvailableAmount -= 1;
+                        return 0;
+                    }
+                }
+            }
+            return -1;
+        }
+
+        public static int GetAvailableAmount(int book_id)
+        {
+            foreach (RegisteredObject obj in _registeredList)
+            {
+                if (obj.Id == book_id)
+                {
+                    return obj.AvailableAmount;
+                }
+            }
+            return -1;
+        }
     }
 
     public class RegisteredObject
@@ -50,6 +77,7 @@ public class RegisteredObject
         public string Info { get; set; }
         public int Id { get; set; }
         public int AvailableAmount { get; set; }
+        public IRegistarable obj { get; set; }
 
         public override string ToString()
         {