diff --git a/tests/test_calculator.py b/tests/test_calculator.py
index 48d48d4..d5364c3 100644
--- a/tests/test_calculator.py
+++ b/tests/test_calculator.py
@@ -3,7 +3,7 @@
 import math
 import unittest
 
-from src.calculator import clamp
+from src.calculator import clamp, percentage
 
 
 class TestClampFunction(unittest.TestCase):
@@ -61,3 +61,30 @@ class TestClampFunction(unittest.TestCase):
     def test_nan_returns_nan(self) -> None:
         result = clamp(math.nan, 0, 10)
         self.assertTrue(math.isnan(result))
+
+
+class TestPercentageFunction(unittest.TestCase):
+
+    def test_valid_percentage(self) -> None:
+        self.assertEqual(percentage(50, 200), 25.0)
+
+    def test_zero_value(self) -> None:
+        self.assertEqual(percentage(0, 100), 0.0)
+
+    def test_full_value(self) -> None:
+        self.assertEqual(percentage(200, 100), 200.0)
+
+    def test_fractional(self) -> None:
+        self.assertAlmostEqual(percentage(1, 3), 33.333333333333336)
+
+    def test_total_zero(self) -> None:
+        with self.assertRaises(ValueError):
+            percentage(50, 0)
+
+    def test_float_arguments(self) -> None:
+        self.assertEqual(percentage(25.5, 100.0), 25.5)
+
+    def test_negative_value(self) -> None:
+        self.assertEqual(percentage(-50, 200), -25.0)
+
+