From 77735da982e8a54262d7f3899bd7bbddbf572632 Mon Sep 17 00:00:00 2001
From: Ishaan Jaffer <ishaanjaffer0324@gmail.com>
Date: Thu, 12 Feb 2026 14:08:31 -0800
Subject: [PATCH] test: add unit test for NPM_CONFIG_CACHE injection in STDIO
 MCP

Verifies that NPM_CONFIG_CACHE is auto-injected when not set, and
preserved when explicitly provided. Also moves the import to module
level per code style rules.
---
 .../mcp_server/mcp_server_manager.py          |  3 +-
 .../mcp_server/test_mcp_server_manager.py     | 39 ++++++++++++++++++-
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
index 68b20c5c3f7..7c211d48abe 100644
--- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
+++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
@@ -31,6 +31,7 @@ from pydantic import AnyUrl
 
 import litellm
 from litellm._logging import verbose_logger
+from litellm.constants import MCP_NPM_CACHE_DIR
 from litellm.exceptions import BlockedPiiEntityError, GuardrailRaisedException
 from litellm.experimental_mcp_client.client import MCPClient
 from litellm.llms.custom_httpx.http_handler import get_async_httpx_client
@@ -897,8 +898,6 @@ class MCPServerManager:
             # In containers the default (~/.npm or /app/.npm) may not exist
             # or be read-only, causing npx to fail with ENOENT.
             if "NPM_CONFIG_CACHE" not in resolved_env:
-                from litellm.constants import MCP_NPM_CACHE_DIR
-
                 resolved_env["NPM_CONFIG_CACHE"] = MCP_NPM_CACHE_DIR
 
             stdio_config: Optional[MCPStdioConfig] = None
diff --git a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
index b4b5811666b..1a50cacd308 100644
--- a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
+++ b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
@@ -112,7 +112,44 @@ class TestMCPServerManager:
         assert client.stdio_config is not None
         assert client.stdio_config["command"] == "node"
         assert client.stdio_config["args"] == ["server.js"]
-        assert client.stdio_config["env"] == {"NODE_ENV": "test"}
+        # NPM_CONFIG_CACHE is injected automatically for container compatibility
+        from litellm.constants import MCP_NPM_CACHE_DIR
+
+        assert client.stdio_config["env"]["NODE_ENV"] == "test"
+        assert client.stdio_config["env"]["NPM_CONFIG_CACHE"] == MCP_NPM_CACHE_DIR
+
+    async def test_create_mcp_client_stdio_injects_npm_config_cache(self):
+        """Test that _create_mcp_client injects NPM_CONFIG_CACHE when not already set,
+        and preserves user-provided NPM_CONFIG_CACHE when present."""
+        from litellm.constants import MCP_NPM_CACHE_DIR
+
+        manager = MCPServerManager()
+
+        # Case 1: NPM_CONFIG_CACHE not set -> should be injected
+        server_no_cache = MCPServer(
+            server_id="stdio-npm-1",
+            name="test_npm_server",
+            url=None,
+            transport=MCPTransport.stdio,
+            command="npx",
+            args=["-y", "@modelcontextprotocol/server-everything"],
+            env={},
+        )
+        client = await manager._create_mcp_client(server_no_cache)
+        assert client.stdio_config["env"]["NPM_CONFIG_CACHE"] == MCP_NPM_CACHE_DIR
+
+        # Case 2: NPM_CONFIG_CACHE already set -> should NOT be overwritten
+        server_with_cache = MCPServer(
+            server_id="stdio-npm-2",
+            name="test_npm_server_custom",
+            url=None,
+            transport=MCPTransport.stdio,
+            command="npx",
+            args=["-y", "@modelcontextprotocol/server-everything"],
+            env={"NPM_CONFIG_CACHE": "/custom/cache"},
+        )
+        client2 = await manager._create_mcp_client(server_with_cache)
+        assert client2.stdio_config["env"]["NPM_CONFIG_CACHE"] == "/custom/cache"
 
     def test_build_stdio_env_only_accepts_x_prefixed_placeholders(self):
         """Ensure only ${X-*} placeholders are substituted from headers."""