diff --git a/tests/chat_model/test_anthropic_chat_model.py b/tests/chat_model/test_anthropic_chat_model.py
index 4a9e3db..12b3ef5 100644
--- a/tests/chat_model/test_anthropic_chat_model.py
+++ b/tests/chat_model/test_anthropic_chat_model.py
@@ -1,4 +1,5 @@
 from typing import Annotated
+from unittest.mock import ANY
 
 import pytest
 from inline_snapshot import snapshot
@@ -11,7 +12,9 @@
 )
 from magentic.chat_model.base import ToolSchemaParseError
 from magentic.chat_model.message import (
+    AssistantMessage,
     DocumentBytes,
+    FunctionResultMessage,
     ImageBytes,
     Message,
     Usage,
@@ -25,6 +28,103 @@
 from magentic.streaming import AsyncStreamedStr, StreamedStr
 
 
+def plus(a: int, b: int) -> int:
+    return a + b
+
+
+@pytest.mark.parametrize(
+    ("message", "expected_anthropic_message"),
+    [
+        (UserMessage("Hello"), {"role": "user", "content": "Hello"}),
+        (AssistantMessage("Hello"), {"role": "assistant", "content": "Hello"}),
+        (
+            AssistantMessage(42),
+            {
+                "role": "assistant",
+                "content": [
+                    {
+                        "type": "tool_use",
+                        "id": ANY,
+                        "name": "return_int",
+                        "input": {"value": 42},
+                    }
+                ],
+            },
+        ),
+        (
+            AssistantMessage(FunctionCall(plus, 1, 2)),
+            {
+                "role": "assistant",
+                "content": [
+                    {
+                        "type": "tool_use",
+                        "id": ANY,
+                        "name": "plus",
+                        "input": {"a": 1, "b": 2},
+                    }
+                ],
+            },
+        ),
+        (
+            AssistantMessage(
+                ParallelFunctionCall(
+                    [FunctionCall(plus, 1, 2), FunctionCall(plus, 3, 4)]
+                )
+            ),
+            {
+                "role": "assistant",
+                "content": [
+                    {
+                        "type": "tool_use",
+                        "id": ANY,
+                        "name": "plus",
+                        "input": {"a": 1, "b": 2},
+                    },
+                    {
+                        "type": "tool_use",
+                        "id": ANY,
+                        "name": "plus",
+                        "input": {"a": 3, "b": 4},
+                    },
+                ],
+            },
+        ),
+        (
+            AssistantMessage(
+                StreamedResponse([StreamedStr(["Hello"]), FunctionCall(plus, 1, 2)])
+            ),
+            {
+                "role": "assistant",
+                "content": [
+                    {"type": "text", "text": "Hello"},
+                    {
+                        "type": "tool_use",
+                        "id": ANY,
+                        "name": "plus",
+                        "input": {"a": 1, "b": 2},
+                    },
+                ],
+            },
+        ),
+        (
+            FunctionResultMessage(3, FunctionCall(plus, 1, 2)),
+            {
+                "role": "user",
+                "content": [
+                    {
+                        "type": "tool_result",
+                        "tool_use_id": ANY,
+                        "content": {"value": 3},
+                    }
+                ],
+            },
+        ),
+    ],
+)
+def test_message_to_anthropic_message(message, expected_anthropic_message):
+    assert message_to_anthropic_message(message) == expected_anthropic_message
+
+
 def test_message_to_anthropic_message_user_image_document_bytes_pdf(document_bytes_pdf):
     image_message = UserMessage([DocumentBytes(document_bytes_pdf)])
     assert message_to_anthropic_message(image_message) == snapshot(