TestClient

examples/chat_with_server.py

@@ -0,0 +1,21 @@
+from fastmcp import FastMCP
+from fastmcp.testing import TestClient
+
+server = FastMCP("test-server")
+
+
+@server.tool()
+def get_the_value_of_schleeb() -> int:
+    return 42
+
+
+async def main():
+    async with TestClient(server) as client:
+        await client.say("What is the value of schleeb?")
+        await client.say("sorry can you repeat that?")
+
+
+if __name__ == "__main__":
+    import asyncio
+
+    asyncio.run(main())

pyproject.toml

@@ -36,6 +36,9 @@ classifiers = [
     "Typing :: Typed",
 ]
 
+[project.optional-dependencies]
+chat = ["marvin>=3.1.0"]
+
 [dependency-groups]
 dev = [
     "copychat>=0.5.2",

src/fastmcp/testing.py

@@ -0,0 +1,37 @@
+from contextlib import ExitStack
+from types import ModuleType
+from typing import Any
+
+from typing_extensions import Self
+
+from fastmcp import FastMCP
+
+
+def _get_agent_framework_module() -> ModuleType:
+    try:
+        import marvin
+    except ImportError:
+        raise ImportError(
+            "please install `fastmcp[chat]` to use TestClient with chat tools"
+        )
+    return marvin
+
+
+class TestClient:
+    def __init__(self, server: FastMCP, agent_options: dict[str, Any] | None = None):
+        self.server = server
+        self._agent_framework = _get_agent_framework_module()
+        self._agent_options = agent_options or {}
+        self._stack = ExitStack()
+
+    async def __aenter__(self) -> Self:
+        self._stack.enter_context(self._agent_framework.Thread())
+        return self
+
+    async def __aexit__(self, exc_type, exc_value, traceback):
+        pass
+
+    async def say(self, message: str) -> None:
+        await self._agent_framework.Agent(
+            mcp_servers=[self.server], **self._agent_options
+        ).run_async(message)