From 65c92ee6bfd6b1e49d701b3b5ebd22a1a34e91ee Mon Sep 17 00:00:00 2001
From: Mrunmayee Daware <165297479+Mrun25@users.noreply.github.com>
Date: Wed, 7 Oct 2026 17:50:39 +0530
Subject: [PATCH] test: cover is_error encoding in anthropic messages adapter

---
 ...al_pass_through_adapters_transformation.py | 77 +++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/tests/unit/llms/anthropic/pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py b/tests/unit/llms/anthropic/pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py
index 06aaa4e61fb..36cc9baba95 100644
--- a/tests/unit/llms/anthropic/pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py
+++ b/tests/unit/llms/anthropic/pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py
@@ -4644,6 +4644,83 @@ def test_tool_result_without_translatable_content_still_answers_its_tool_use(too
     assert result[0]["role"] == "assistant"
 
 
+def test_tool_result_is_error_is_encoded_in_string_content():
+    adapter = LiteLLMAnthropicMessagesAdapter()
+
+    result = adapter.translate_anthropic_messages_to_openai(
+        messages=[
+            _anthropic_tool_use_turn("toolu_01"),
+            {
+                "role": "user",
+                "content": [
+                    {
+                        "type": "tool_result",
+                        "tool_use_id": "toolu_01",
+                        "content": "deploy failed",
+                        "is_error": True,
+                    }
+                ],
+            },
+        ]
+    )
+
+    assert result[1] == {
+        "role": "tool",
+        "tool_call_id": "toolu_01",
+        "content": "[tool error] deploy failed",
+    }
+
+
+def test_tool_result_is_error_puts_the_marker_first_in_part_lists():
+    adapter = LiteLLMAnthropicMessagesAdapter()
+
+    result = adapter.translate_anthropic_messages_to_openai(
+        messages=[
+            _anthropic_tool_use_turn("toolu_01"),
+            {
+                "role": "user",
+                "content": [
+                    {
+                        "type": "tool_result",
+                        "tool_use_id": "toolu_01",
+                        "content": [{"type": "text", "text": "boom"}, _tool_reference_block()],
+                        "is_error": True,
+                    }
+                ],
+            },
+        ]
+    )
+
+    assert result[1]["content"] == [
+        {"type": "text", "text": "[tool error] "},
+        {"type": "text", "text": "boom"},
+        {"type": "tool_reference", "tool_name": "WebFetch"},
+    ]
+
+
+def test_tool_result_without_is_error_keeps_content_unchanged():
+    adapter = LiteLLMAnthropicMessagesAdapter()
+
+    result = adapter.translate_anthropic_messages_to_openai(
+        messages=[
+            _anthropic_tool_use_turn("toolu_01"),
+            {
+                "role": "user",
+                "content": [
+                    {
+                        "type": "tool_result",
+                        "tool_use_id": "toolu_01",
+                        "content": "deploy succeeded",
+                        "is_error": False,
+                    }
+                ],
+            },
+        ]
+    )
+
+    assert result[1]["content"] == "deploy succeeded"
+
+
 def _openai_response_with_usage(usage: Usage) -> ModelResponse:
     return ModelResponse(
         id="resp_web_search",