diff --git a/tosfs/retry.py b/tosfs/retry.py
index 7197f6d..fc0d5f2 100644
--- a/tosfs/retry.py
+++ b/tosfs/retry.py
@@ -33,14 +33,14 @@
 
 from tosfs.exceptions import TosfsError
 
-CONFLICT_CODE = "409"
-TOO_MANY_REQUESTS_CODE = "429"
-SERVICE_UNAVAILABLE = "503"
+CONFLICT_CODE = 409
+TOO_MANY_REQUESTS_CODE = 429
+SERVICE_UNAVAILABLE = 503
 
 TOS_SERVER_RETRYABLE_STATUS_CODES = {
     CONFLICT_CODE,
     TOO_MANY_REQUESTS_CODE,
-    "500",  # INTERNAL_SERVER_ERROR,
+    500,  # INTERNAL_SERVER_ERROR,
     SERVICE_UNAVAILABLE,
 }
 
@@ -111,13 +111,18 @@ def retryable_func_executor(
                 except InterruptedError as ie:
                     raise TosfsError(f"Request {func} interrupted.") from ie
             else:
-                raise e
+                _rethrow_retryable_exception(e)
         # Note: maybe not all the retryable exceptions are warped by `TosError`
         # Will pay attention to those cases
         except Exception as e:
             raise TosfsError(f"{e}") from e
 
 
+def _rethrow_retryable_exception(e: TosError) -> None:
+    """For debug purpose."""
+    raise e
+
+
 def is_retryable_exception(e: TosError) -> bool:
     """Check if the exception is retryable."""
     return _is_retryable_tos_server_exception(e) or _is_retryable_tos_client_exception(
diff --git a/tosfs/tests/test_retry.py b/tosfs/tests/test_retry.py
new file mode 100644
index 0000000..ab13630
--- /dev/null
+++ b/tosfs/tests/test_retry.py
@@ -0,0 +1,82 @@
+# ByteDance Volcengine EMR, Copyright 2024.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# ByteDance Volcengine EMR, Copyright 2024.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest.mock import Mock
+
+import pytest
+import requests
+from tos.exceptions import TosClientError, TosServerError
+from tos.http import Response
+from urllib3.exceptions import ProtocolError
+
+from tosfs.retry import is_retryable_exception
+
+mock_resp = Mock(spec=requests.Response)
+
+mock_resp.status_code = 429
+mock_resp.headers = {"content-length": "123", "x-tos-request-id": "test-id"}
+mock_resp.iter_content = Mock(return_value=[b"chunk1", b"chunk2", b"chunk3"])
+mock_resp.json = Mock(return_value={"key": "value"})
+
+response = Response(mock_resp)
+
+
+@pytest.mark.parametrize(
+    ("exception", "expected"),
+    [
+        (
+            TosServerError(
+                response,
+                "Exceed account external rate limit. Too much throughput in a "
+                "short period of time, please slow down.",
+                "ExceedAccountExternalRateLimit",
+                "KmsJSKDKhjasdlKmsduwRETYHB",
+                "",
+                "0004-00000001",
+            ),
+            True,
+        ),
+        (
+            TosClientError(
+                "http request timeout",
+                ConnectionError(
+                    ProtocolError(
+                        "Connection aborted.",
+                        ConnectionResetError(104, "Connection reset by peer"),
+                    )
+                ),
+            ),
+            True,
+        ),
+    ],
+)
+def test_is_retry_exception(
+    exception,
+    expected,
+):
+    assert is_retryable_exception(exception) == expected