fixes tests for z-score

exercises/2024/ChatGPT/z_score/sol/z_score.py

@@ -1,10 +1,15 @@
 from typing import List
 import math
 
+
 class ZScoreCalculator:
     def __init__(self, data: List[float]):
-        self.mean = sum(data) / len(data) if data else 0
-        self.std_dev = math.sqrt(sum((x - self.mean) ** 2 for x in data) / len(data)) if data else 0
+        self.mean = sum(data) / len(data) if data else math.nan
+        self.std_dev = (
+            math.sqrt(sum((x - self.mean) ** 2 for x in data) / len(data))
+            if data
+            else math.nan
+        )
 
     def calculate_z_score(self, x: float) -> float:
-        return (x - self.mean) / self.std_dev if self.std_dev != 0 else 0
+        return (x - self.mean) / self.std_dev if self.std_dev != 0 else 0

exercises/2024/ChatGPT/z_score/test/test_z_score.py

@@ -1,18 +1,24 @@
 import unittest
+import math
 
 from z_score import ZScoreCalculator
 
+
 class TestZScoreCalculator(unittest.TestCase):
-    
+
     def testZScoreCalculator(self):
         calculator = ZScoreCalculator([10, 20, 30, 40, 50])
         self.assertAlmostEqual(0.0, calculator.calculate_z_score(30), places=5)
-        self.assertAlmostEqual(1.414213562373095, calculator.calculate_z_score(55), places=5)
-        self.assertAlmostEqual(-1.414213562373095, calculator.calculate_z_score(5), places=5)
+        self.assertAlmostEqual(
+            1.7677669529663687, calculator.calculate_z_score(55), places=5
+        )
+        self.assertAlmostEqual(
+            -1.7677669529663687, calculator.calculate_z_score(5), places=5
+        )
 
     def testZScoreCalculatorEmpty(self):
         calculator = ZScoreCalculator([])
-        self.assertEqual(0, calculator.calculate_z_score(10))
+        self.assertTrue(math.isnan(calculator.calculate_z_score(10)))
 
     def testZScoreCalculatorSingleElement(self):
         calculator = ZScoreCalculator([5])
@@ -22,5 +28,6 @@ def testZScoreCalculatorRepeatedValues(self):
         calculator = ZScoreCalculator([5, 5, 5, 5, 5])
         self.assertEqual(0, calculator.calculate_z_score(5))
 
-if __name__ == '__main__':
-    unittest.main()
+
+if __name__ == "__main__":
+    unittest.main()