diff --git a/python/Quiz_4.py b/python/Quiz_4.py
index 454f0b6..ea64cb1 100644
--- a/python/Quiz_4.py
+++ b/python/Quiz_4.py
@@ -149,16 +149,17 @@ def insertPC(_conn, _maker, _model, _speed, _ram, _hd, _price):
     print(l)
     cursor = _conn.cursor()
 
-    cursor.execute('DELETE FROM pc WHERE model = {};'.format(_model))
+    cursor.execute('DELETE FROM pc WHERE model = ?;', (_model,))
 
-    cursor.execute('DELETE FROM product WHERE model = {};'.format(_model))
+    cursor.execute('DELETE FROM product WHERE model = ?;', (_model,))
 
     cursor.execute(
-        'INSERT INTO pc(model, speed, ram, hd, price) VALUES(\'{}\', {}, {}, {}, {});'.format(
-            _model, _speed, _ram, _hd, _price))
+        'INSERT INTO pc(model, speed, ram, hd, price) VALUES(?, ?, ?, ?, ?);',
+        (_model, _speed, _ram, _hd, _price)
+    )
 
-    cursor.execute('INSERT INTO product(maker, model, TYPE) VALUES(\'{}\', {}, \'{}\');'.format(
-        _maker, _model, 'PC'))
+    cursor.execute('INSERT INTO product(maker, model, TYPE) VALUES(?, ?, ?);',
+        (_maker, _model, 'PC'))
 
     _conn.commit()
     print("++++++++++++++++++++++++++++++++++")
@@ -179,7 +180,7 @@ def updatePrinter(_conn, _model, _price):
     cursor = _conn.cursor()
     # Fixed typo from original code: exucte -> execute
     cursor.execute(
-        'UPDATE printer SET price = {} WHERE model = {};'.format(_price, _model))
+        'UPDATE printer SET price = ? WHERE model = ?;', (_price, _model))
     _conn.commit()
 
     print("++++++++++++++++++++++++++++++++++")
@@ -198,7 +199,7 @@ def deleteLaptop(_conn, _model):
     print(l)
 
     cursor = _conn.cursor()
-    cursor.execute('DELETE FROM laptop WHERE model = {}'.format(_model))
+    cursor.execute('DELETE FROM laptop WHERE model = ?', (_model,))
     _conn.commit()
 
     print("++++++++++++++++++++++++++++++++++")
diff --git a/python/test_quiz_4.py b/python/test_quiz_4.py
new file mode 100644
index 0000000..b49e552
--- /dev/null
+++ b/python/test_quiz_4.py
@@ -0,0 +1,98 @@
+import unittest
+import sqlite3
+from Quiz_4 import insertPC, updatePrinter, deleteLaptop
+
+class TestQuiz4(unittest.TestCase):
+    def setUp(self):
+        # Create an in-memory database for testing
+        self.conn = sqlite3.connect(':memory:')
+        self.cursor = self.conn.cursor()
+
+        # Create the necessary tables
+        self.cursor.execute('''
+            CREATE TABLE pc (
+                model INTEGER PRIMARY KEY,
+                speed REAL,
+                ram INTEGER,
+                hd INTEGER,
+                price INTEGER
+            )
+        ''')
+
+        self.cursor.execute('''
+            CREATE TABLE product (
+                maker TEXT,
+                model INTEGER PRIMARY KEY,
+                type TEXT
+            )
+        ''')
+
+        self.cursor.execute('''
+            CREATE TABLE printer (
+                model INTEGER PRIMARY KEY,
+                color TEXT,
+                type TEXT,
+                price INTEGER
+            )
+        ''')
+
+        self.cursor.execute('''
+            CREATE TABLE laptop (
+                model INTEGER PRIMARY KEY,
+                speed REAL,
+                ram INTEGER,
+                hd INTEGER,
+                screen REAL,
+                price INTEGER
+            )
+        ''')
+
+        self.conn.commit()
+
+    def tearDown(self):
+        self.conn.close()
+
+    def test_insertPC(self):
+        # Test inserting a PC
+        insertPC(self.conn, 'A', 1001, 2.66, 1024, 250, 2114)
+
+        # Verify insertion into pc table
+        self.cursor.execute('SELECT * FROM pc WHERE model = 1001')
+        pc_result = self.cursor.fetchone()
+        self.assertIsNotNone(pc_result)
+        self.assertEqual(pc_result, (1001, 2.66, 1024, 250, 2114))
+
+        # Verify insertion into product table
+        self.cursor.execute('SELECT * FROM product WHERE model = 1001')
+        product_result = self.cursor.fetchone()
+        self.assertIsNotNone(product_result)
+        self.assertEqual(product_result, ('A', 1001, 'PC'))
+
+    def test_updatePrinter(self):
+        # Insert a printer first
+        self.cursor.execute("INSERT INTO printer (model, color, type, price) VALUES (3001, 'true', 'ink-jet', 99)")
+        self.conn.commit()
+
+        # Test updating the printer
+        updatePrinter(self.conn, 3001, 150)
+
+        # Verify update
+        self.cursor.execute('SELECT price FROM printer WHERE model = 3001')
+        price_result = self.cursor.fetchone()[0]
+        self.assertEqual(price_result, 150)
+
+    def test_deleteLaptop(self):
+        # Insert a laptop first
+        self.cursor.execute("INSERT INTO laptop (model, speed, ram, hd, screen, price) VALUES (2001, 2.0, 2048, 240, 20.1, 3150)")
+        self.conn.commit()
+
+        # Test deleting the laptop
+        deleteLaptop(self.conn, 2001)
+
+        # Verify deletion
+        self.cursor.execute('SELECT * FROM laptop WHERE model = 2001')
+        laptop_result = self.cursor.fetchone()
+        self.assertIsNone(laptop_result)
+
+if __name__ == '__main__':
+    unittest.main()