Add unit tests for factorial.py

Author: Qasim-Umar-Khan

maths/test_factorial.py

@@ -0,0 +1,22 @@
+import unittest
+from factorial import factorial
+
+class TestFactorial(unittest.TestCase):
+
+    def test_zero(self):
+        self.assertEqual(factorial(0), 1)
+
+    def test_positive_integers(self):
+        self.assertEqual(factorial(1), 1)
+        self.assertEqual(factorial(5), 120)
+        self.assertEqual(factorial(7), 5040)
+
+    def test_large_number(self):
+        self.assertEqual(factorial(10), 3628800)
+
+    def test_negative_number(self):
+        with self.assertRaises(ValueError):
+            factorial(-3)
+
+if __name__ == '__main__':
+    unittest.main()