Add test to catch warning divide-by-zero raised by process_diagonal

Author: NimaSarajpoor

tests/test_core.py

@@ -1,6 +1,7 @@
 import functools
 import math
 import os
+import warnings
 from unittest.mock import patch
 
 import naive
@@ -1753,3 +1754,16 @@ def test_process_isconstant_2d():
     T_subseq_isconstant_comp = core.process_isconstant(T, m, T_subseq_isconstant)
 
     npt.assert_array_equal(T_subseq_isconstant_ref, T_subseq_isconstant_comp)
+
+
+def test_preprocess_diagonal_std_inverse():
+    T = np.random.rand(64)
+    m = 3
+    T[:m] = np.nan
+
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        core.preprocess_diagonal(T, m)
+        for item in w:
+            if issubclass(item.category, RuntimeWarning):
+                assert "divide by zero encountered in divide" not in str(item.message)