Add tests for functools.partial support

Covers tools, prompts, and resources:
- Sync and async partials as tools
- Name preservation with update_wrapper
- Partial without update_wrapper (uses underlying fn name)
- Registration via add_tool and @mcp.tool() decorator
- Registration via @mcp.prompt() and @mcp.resource() decorators

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: strawgate

tests/tools/tool/test_partial.py

@@ -0,0 +1,129 @@
+"""Tests for functools.partial support as tools, prompts, and resources.
+
+See https://github.com/PrefectHQ/fastmcp/issues/3266
+"""
+
+import functools
+
+from mcp.types import TextContent
+
+from fastmcp import Client, FastMCP
+from fastmcp.tools.function_tool import FunctionTool as Tool
+
+
+class TestPartialTool:
+    """Test tools created from functools.partial objects."""
+
+    async def test_partial_sync(self):
+        def add(x: int, y: int) -> int:
+            return x + y
+
+        partial_add = functools.partial(add, y=10)
+        functools.update_wrapper(partial_add, add)
+
+        tool = Tool.from_function(partial_add)
+        result = await tool.run({"x": 5})
+        assert result.content == [TextContent(type="text", text="15")]
+
+    async def test_partial_async(self):
+        async def multiply(x: int, factor: int) -> int:
+            return x * factor
+
+        partial_mul = functools.partial(multiply, factor=3)
+        functools.update_wrapper(partial_mul, multiply)
+
+        tool = Tool.from_function(partial_mul)
+        result = await tool.run({"x": 7})
+        assert result.content == [TextContent(type="text", text="21")]
+
+    async def test_partial_preserves_name(self):
+        def greet(name: str, greeting: str = "Hello") -> str:
+            """Greet someone."""
+            return f"{greeting}, {name}!"
+
+        partial_greet = functools.partial(greet, greeting="Hi")
+        functools.update_wrapper(partial_greet, greet)
+
+        tool = Tool.from_function(partial_greet)
+        assert tool.name == "greet"
+        assert tool.description == "Greet someone."
+
+    async def test_partial_without_update_wrapper(self):
+        def add(x: int, y: int) -> int:
+            return x + y
+
+        partial_add = functools.partial(add, y=10)
+
+        tool = Tool.from_function(partial_add, name="add_ten")
+        result = await tool.run({"x": 5})
+        assert result.content == [TextContent(type="text", text="15")]
+
+    async def test_partial_with_add_tool(self):
+        mcp = FastMCP("test")
+
+        def greet(name: str, greeting: str = "Hello") -> str:
+            return f"{greeting}, {name}!"
+
+        partial_greet = functools.partial(greet, greeting="Hey")
+        functools.update_wrapper(partial_greet, greet)
+
+        mcp.add_tool(partial_greet)
+
+        result = await mcp.call_tool("greet", {"name": "World"})
+        assert result.content == [TextContent(type="text", text="Hey, World!")]
+
+    async def test_partial_with_server_tool_decorator(self):
+        mcp = FastMCP("test")
+
+        def add(x: int, y: int) -> int:
+            return x + y
+
+        partial_add = functools.partial(add, y=100)
+        functools.update_wrapper(partial_add, add)
+
+        mcp.tool(partial_add)
+
+        result = await mcp.call_tool("add", {"x": 5})
+        assert result.content == [TextContent(type="text", text="105")]
+
+
+class TestPartialPrompt:
+    """Test prompts created from functools.partial objects."""
+
+    async def test_partial_prompt_with_decorator(self):
+        """Partial can be registered via @mcp.prompt() decorator."""
+        mcp = FastMCP("test")
+
+        def greet_prompt(name: str, lang: str) -> str:
+            return f"Say hello to {name} in {lang}."
+
+        partial_greet = functools.partial(greet_prompt, lang="French")
+        functools.update_wrapper(partial_greet, greet_prompt)
+
+        mcp.prompt(partial_greet)
+
+        async with Client(mcp) as client:
+            result = await client.get_prompt("greet_prompt", {"name": "Alice"})
+            assert "Alice" in str(result.messages[0])
+            assert "French" in str(result.messages[0])
+
+
+class TestPartialResource:
+    """Test resources created from functools.partial objects."""
+
+    async def test_partial_resource_with_decorator(self):
+        """Partial can be registered via @mcp.resource() decorator."""
+        mcp = FastMCP("test")
+
+        def get_data(key: str, fmt: str = "text") -> str:
+            return f"{key} in {fmt} format"
+
+        partial_data = functools.partial(get_data, fmt="json")
+        functools.update_wrapper(partial_data, get_data)
+
+        mcp.resource("data://{key}")(partial_data)
+
+        async with Client(mcp) as client:
+            content = await client.read_resource("data://users")
+            assert "users" in str(content)
+            assert "json" in str(content)