test(sveta): Write tests for percentage function

Outcome: done
Changed: tests/test_calculator.py:1 (import), tests/test_calculator.py:66-96 (new TestPercentageFunction class)
Verified by: `make verify` — exit 0, Ran 23 tests, OK
Findings: tests/test_calculator.py:66-96 — TestPercentageFunction class added with 7 test methods (valid_percentage, zero_value, full_value, fractional, total_zero, float_arguments, negative_value). All 23 tests pass.
Open: none
Confidence: high — all acceptance criteria met, verification passed

Typosaurus-Run: ff52a86851934fd293e2f4493c5a9a46
Typosaurus-Node: 7edce3239d434d36aed06535aae0d0ad
Typosaurus-Agent: @sveta
Refs: #16

tests/test_calculator.py

@@ -3,7 +3,7 @@
 import math
 import unittest
 
-from src.calculator import clamp, variance
+from src.calculator import clamp, percentage, variance
 
 
 class TestClampFunction(unittest.TestCase):
@@ -63,6 +63,31 @@ class TestClampFunction(unittest.TestCase):
         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)
+
+
 class TestVarianceFunction(unittest.TestCase):
 
     def test_empty_list_raises_value_error(self) -> None:
@@ -94,3 +119,4 @@ class TestVarianceFunction(unittest.TestCase):
         self.assertEqual(variance((1, 2, 3, 4, 5)), 2.0)
 
 
+