Validate hypertoroidal Fourier coefficient counts

src/pyrecest/filters/hypertoroidal_fourier_filter.py

@@ -20,6 +20,7 @@
 )
 from pyrecest.distributions.hypertorus.hypertoroidal_fourier_distribution import (
     HypertoroidalFourierDistribution,
+    _normalize_coefficient_shape,
 )
 
 from .abstract_filter import AbstractFilter
@@ -56,9 +57,11 @@ def __init__(self, n_coefficients, transformation="sqrt"):
                 "HypertoroidalFourierFilter is not supported on the "
                 f"{pyrecest.backend.__backend_name__} backend."
             )
-        if isinstance(n_coefficients, int):
-            n_coefficients = (n_coefficients,)
-        n_coefficients = tuple(int(n) for n in n_coefficients)
+        n_coefficients = _normalize_coefficient_shape(
+            n_coefficients,
+            "n_coefficients",
+            require_odd=True,
+        )
         dim = len(n_coefficients)
 
         # Build a uniform HFD directly (only the DC component is non-zero)

tests/filters/test_hypertoroidal_fourier_filter_coefficient_validation.py

@@ -0,0 +1,39 @@
+import unittest
+
+import numpy as np
+
+import pyrecest.backend
+from pyrecest.filters.hypertoroidal_fourier_filter import HypertoroidalFourierFilter
+
+
+@unittest.skipIf(
+    pyrecest.backend.__backend_name__ in ("jax", "pytorch"),
+    reason="HypertoroidalFourierFilter is not supported on this backend",
+)
+class TestHypertoroidalFourierFilterCoefficientValidation(unittest.TestCase):
+    def test_accepts_numpy_integer_scalar(self):
+        fourier_filter = HypertoroidalFourierFilter(np.int64(11))
+
+        self.assertEqual(fourier_filter.filter_state.coeff_mat.shape, (11,))
+
+    def test_rejects_values_that_would_be_silently_reinterpreted(self):
+        invalid_values = (
+            True,
+            "11",
+            (),
+            (11.5,),
+            (11.0,),
+        )
+
+        for value in invalid_values:
+            with self.subTest(value=value):
+                with self.assertRaises((TypeError, ValueError)):
+                    HypertoroidalFourierFilter(value)
+
+    def test_rejects_nonpositive_or_even_coefficient_counts(self):
+        invalid_values = (0, -1, 10, (11, 0), (11, 12))
+
+        for value in invalid_values:
+            with self.subTest(value=value):
+                with self.assertRaisesRegex(ValueError, "n_coefficients"):
+                    HypertoroidalFourierFilter(value)