diff --git a/tests/test_litellm/responses/litellm_completion_transformation/__init__.py b/tests/test_litellm/responses/litellm_completion_transformation/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/test_litellm/responses/litellm_completion_transformation/test_handler_json_arguments.py b/tests/test_litellm/responses/litellm_completion_transformation/test_handler_json_arguments.py
new file mode 100644
index 00000000000..3eb05fdaabf
--- /dev/null
+++ b/tests/test_litellm/responses/litellm_completion_transformation/test_handler_json_arguments.py
@@ -0,0 +1,252 @@
+"""
+Tests for LiteLLMCompletionTransformationHandler argument validation.
+
+Tests the _ensure_all_tool_calls_have_valid_json_arguments function that
+validates and fixes tool_calls arguments in messages for domestic models.
+"""
+
+import json
+import os
+import sys
+import unittest
+
+sys.path.insert(0, os.path.abspath("../../.."))
+
+from litellm.responses.litellm_completion_transformation.handler import (
+    LiteLLMCompletionTransformationHandler,
+)
+
+
+class TestEnsureToolCallsValidJsonArguments(unittest.TestCase):
+    """Test _ensure_all_tool_calls_have_valid_json_arguments static method."""
+
+    def setUp(self):
+        """Set up handler instance."""
+        self.handler = LiteLLMCompletionTransformationHandler()
+
+    def test_valid_json_arguments(self):
+        """Test that valid JSON arguments are preserved."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "test_func",
+                            "arguments": '{"key": "value"}',
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], '{"key": "value"}')
+
+    def test_empty_arguments(self):
+        """Test that empty arguments are converted to '{}'."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "test_func",
+                            "arguments": "",
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], "{}")
+
+    def test_none_arguments(self):
+        """Test that None arguments are converted to '{}'."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "test_func",
+                            "arguments": None,
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], "{}")
+
+    def test_invalid_json_arguments(self):
+        """Test that invalid JSON arguments are converted to '{}'."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "test_func",
+                            "arguments": "not a valid json",
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], "{}")
+
+    def test_dict_arguments_converted_to_json(self):
+        """Test that dict arguments are converted to JSON string."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "test_func",
+                            "arguments": {"key": "value", "number": 42},
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        # dict should be converted to JSON string
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], '{"key": "value", "number": 42}')
+
+    def test_whitespace_arguments(self):
+        """Test that whitespace-only arguments are converted to '{}'."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "test_func",
+                            "arguments": "   ",
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], "{}")
+
+    def test_non_assistant_messages_preserved(self):
+        """Test that non-assistant messages are not modified."""
+        messages = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": "Hi there"},
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(len(result), 2)
+        self.assertEqual(result[0]["role"], "user")
+        self.assertEqual(result[1]["role"], "assistant")
+
+    def test_assistant_without_tool_calls_preserved(self):
+        """Test that assistant messages without tool_calls are preserved."""
+        messages = [
+            {"role": "assistant", "content": "No tools here"},
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["content"], "No tools here")
+
+    def test_multiple_tool_calls_in_one_message(self):
+        """Test handling of multiple tool calls in a single message."""
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_1",
+                        "type": "function",
+                        "function": {
+                            "name": "func1",
+                            "arguments": '{"valid": true}',
+                        },
+                    },
+                    {
+                        "id": "call_2",
+                        "type": "function",
+                        "function": {
+                            "name": "func2",
+                            "arguments": "invalid",
+                        },
+                    },
+                    {
+                        "id": "call_3",
+                        "type": "function",
+                        "function": {
+                            "name": "func3",
+                            "arguments": None,
+                        },
+                    },
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        # First should be preserved (valid)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], '{"valid": true}')
+        # Second should be fixed (invalid -> {})
+        self.assertEqual(result[0]["tool_calls"][1]["function"]["arguments"], "{}")
+        # Third should be fixed (None -> {})
+        self.assertEqual(result[0]["tool_calls"][2]["function"]["arguments"], "{}")
+
+    def test_empty_messages_list(self):
+        """Test handling of empty messages list."""
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments([])
+        self.assertEqual(result, [])
+
+    def test_complex_valid_json(self):
+        """Test that complex valid JSON is preserved."""
+        complex_json = json.dumps({
+            "nested": {
+                "deep": {
+                    "value": [1, 2, 3]
+                }
+            },
+            "string": "with \"escaped\" quotes",
+            "number": 123.456
+        })
+        messages = [
+            {
+                "role": "assistant",
+                "content": None,
+                "tool_calls": [
+                    {
+                        "id": "call_123",
+                        "type": "function",
+                        "function": {
+                            "name": "complex_func",
+                            "arguments": complex_json,
+                        },
+                    }
+                ],
+            }
+        ]
+        result = self.handler._ensure_all_tool_calls_have_valid_json_arguments(messages)
+        self.assertEqual(result[0]["tool_calls"][0]["function"]["arguments"], complex_json)
+
+
+if __name__ == "__main__":
+    unittest.main()
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