add roundtrip serialization test for List[List[Dict[int, np.ndarray]]]

tests/test_custom_serialization.py

@@ -149,3 +149,24 @@ def check(*, actual, expected):
 
     _roundtrip(mnt, custom_serialize, custom_deserialize, check)
     _roundtrip(mdc, custom_serialize, custom_deserialize, check)
+
+
+def test_nested_array_dict_int_keys(custom_serialize, custom_deserialize):
+    N = 4
+    M = 3
+
+    def check(*, actual, expected):
+        assert isinstance(actual, type(expected))
+        assert len(actual) == N
+        for xs in actual:
+            assert len(xs) == M
+            for i, arr in xs.items():
+                assert isinstance(i, int)
+                _check_array_like(actual=arr, expected=np.ones(i))
+
+  m: List[List[Dict[int, np.ndarray]]] = [[
+      [{i:np.ones(i) for i in range(M)]
+      for _ in range(N)
+  ]]
+
+  _roundtrip(m, custom_serialize, custom_deserialize, check)