mcp-testing

MCP Testing Skill

Modern testing strategies for Model Context Protocol (MCP) servers developed in VS Code using TypeScript, Bun, and Vitest.

Unit Testing with Vitest & In-Memory Transport

Setup Minimal Test Environment

import { describe, it, expect, beforeEach } from "vitest";
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { InMemoryTransport } from "@modelcontextprotocol/sdk/testing/inMemoryTransport.js";
import { RaindropMCPService } from "../src/services/raindropmcp.service.js";

describe("RaindropMCPService Tools", () => {
  let service: RaindropMCPService;
  let transport: InMemoryTransport;
  let client: Client;

  beforeEach(async () => {
    service = new RaindropMCPService();
    transport = new InMemoryTransport(service.getServer());
    client = new Client(
      {
        name: "test-client",
        version: "1.0.0",
      },
      { capabilities: {} },
    );
    await client.connect(transport);
  });

  it("should list available tools", async () => {
    const tools = await client.listTools();
    expect(tools.tools.length).toBeGreaterThan(0);
    expect(tools.tools.map((t) => t.name)).toContain("collection_list");
  });

  it("should call a tool with valid input", async () => {
    const result = await client.callTool({
      name: "collection_list",
      arguments: {},
    });
    expect(result).toBeDefined();
    expect(result.content).toBeDefined();
  });
});

Key Testing Patterns

1. In-Memory Transport: Use for unit tests—no subprocess overhead, direct method invocation
2. Server Capabilities: Verify manifest before running tool tests
3. Mock Context: Provide mock RaindropService for isolated tool testing
4. Error Handling: Test both success and error paths with Zod validation

Integration Testing with MCP Inspector

Launch Inspector in VS Code

1. Terminal > Run Task > "Debug HTTP Server with Inspector" (or STDIO variant)
   • Opens Inspector at http://localhost:3000 (or via auto-opened browser)
   • Live tool/resource exploration with bidirectional message capture