diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java
index 8ddecb9..ad27bfb 100644
--- a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java
@@ -21,4 +21,7 @@ public class Book {
     private String description ;
     private String language;
 
+    public void addStock(Integer copyToAdd){
+        this.stock += copyToAdd;
+    }
 }
diff --git a/src/test/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/BookTest.java b/src/test/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/BookTest.java
index 5fc5eec..db21e1d 100644
--- a/src/test/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/BookTest.java
+++ b/src/test/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/BookTest.java
@@ -3,6 +3,7 @@ package fr.iut_fbleau.but3.dev62.mylibrary.book.entity;
 import fr.iut_fbleau.but3.dev62.mylibrary.book.BookDTO;
 import fr.iut_fbleau.but3.dev62.mylibrary.book.converter.BookConverter;
 import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 
 import java.time.LocalDate;
@@ -51,4 +52,37 @@ public class BookTest {
         assertEquals(description, book.getDescription());
         assertEquals(language, book.getLanguage());
     }
+
+    @Nested
+    @DisplayName("Loyalty Points Tests")
+    class StockTests {
+
+        @Test
+        @DisplayName("addCopy should correctly increment stocks")
+        void testAddCopy() {
+            Book book =Book.builder()
+                    .stock(5)
+                    .build();
+            Integer copyToAdd = 5;
+            Integer copyExpected = 10;
+
+            book.addStock(copyToAdd);
+
+            assertEquals(copyExpected, book.getStock());
+        }
+
+        @Test
+        @DisplayName("addCopy should correctly increment zero points correctly")
+        void testAddZeroToCopy() {
+            Book book =Book.builder()
+                    .stock(5)
+                    .build();
+            Integer copyToAdd = 0;
+            Integer copyExpected = 5;
+
+            book.addStock(copyToAdd);
+
+            assertEquals(copyExpected, book.getStock());
+        }
+    }
 }