gh-154945: add regression test for NormalDist.quantiles(0)

Adds test_quantiles_invalid_n to verify that NormalDist.quantiles(n)
raises StatisticsError when n < 1, mirroring the module-level quantiles()
validation. Currently fails (test is red) — quantiles(0) silently returns []
instead of raising.

Author: nikolauspschuetz

Lib/test/test_statistics.py

@@ -3105,6 +3105,13 @@ def test_quantiles(self):
             self.assertTrue(all(math.isclose(e, a, abs_tol=0.0001)
                             for e, a in zip(expected, actual)))
 
+    def test_quantiles_invalid_n(self):
+        # quantiles(n) should reject n < 1
+        Z = self.module.NormalDist()
+        with self.assertRaises(self.module.StatisticsError) as cm:
+            Z.quantiles(0)
+        self.assertEqual(str(cm.exception), 'n must be at least 1')
+
     def test_overlap(self):
         NormalDist = self.module.NormalDist