ts-mcp-template/tests/stdio.test.ts

import { readFile } from "node:fs/promises";
import { dirname, resolve } from "node:path";
import { fileURLToPath } from "node:url";
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
import { describe, expect, it } from "vitest";
import { EXAMPLE_ECHO_TOOL_NAME } from "../src/capabilities/index.js";

const testsDir = dirname(fileURLToPath(import.meta.url));
const projectRoot = resolve(testsDir, "..");
const stdioEntryPath = resolve(projectRoot, "src/stdio.ts");
const packageJsonPath = resolve(projectRoot, "package.json");

type StdioCommandConfig = {
  mcp?: {
    stdio?: {
      command?: string;
      args?: string[];
    };
  };
  scripts?: Record<string, string>;
};

async function readStdioCommandConfig(): Promise<{ command: string; args: string[] }> {
  const packageJsonRaw = await readFile(packageJsonPath, "utf8");
  const packageJson = JSON.parse(packageJsonRaw) as StdioCommandConfig;

  return {
    command: packageJson.mcp?.stdio?.command ?? "node",
    args: packageJson.mcp?.stdio?.args ?? [],
  };
}

async function createConnectedStdioClient(): Promise<{
  client: Client;
  transport: StdioClientTransport;
}> {
  const stdioCommand = await readStdioCommandConfig();
  const transport = new StdioClientTransport({
    command: stdioCommand.command,
    args: stdioCommand.args,
    cwd: projectRoot,
    stderr: "pipe",
  });
  const client = new Client(
    { name: "stdio-test-client", version: "0.0.0" },
    { capabilities: {} },
  );

  await client.connect(transport);
  return { client, transport };
}

describe("stdio entrypoint", () => {
  it("starts over stdio and keeps startup diagnostics on stderr", async () => {
    const stdioCommand = await readStdioCommandConfig();
    const transport = new StdioClientTransport({
      command: stdioCommand.command,
      args: stdioCommand.args,
      cwd: projectRoot,
      stderr: "pipe",
    });
    const stderrMessages: string[] = [];
    const stderr = transport.stderr;
    stderr?.on("data", (chunk) => {
      stderrMessages.push(chunk.toString());
    });
    const client = new Client(
      { name: "stdio-test-client", version: "0.0.0" },
      { capabilities: {} },
    );

    await client.connect(transport);
    const tools = await client.listTools();

    expect(tools.tools.map((tool) => tool.name)).toContain(EXAMPLE_ECHO_TOOL_NAME);
    expect(stderrMessages.join("")).toContain("MCP stdio server started");

    await client.close();
    await transport.close();
  });

  it("rejects invalid tool calls over stdio transport", async () => {
    const { client, transport } = await createConnectedStdioClient();

    const missingToolResult = await client.callTool({
      name: "template.missing-tool",
      arguments: {},
    });
    const invalidInputResult = await client.callTool({
      name: EXAMPLE_ECHO_TOOL_NAME,
      arguments: { uppercase: true },
    });

    expect(missingToolResult.isError).toBe(true);
    expect(JSON.stringify(missingToolResult.content)).toMatch(/not found|unknown/i);
    expect(invalidInputResult.isError).toBe(true);
    expect(JSON.stringify(invalidInputResult.content)).toMatch(/message|required|invalid/i);

    await client.close();
    await transport.close();
  });

  it("publishes a non-npm stdio launch command for MCP clients", async () => {
    const packageJsonRaw = await readFile(packageJsonPath, "utf8");
    const packageJson = JSON.parse(packageJsonRaw) as StdioCommandConfig;

    expect(packageJson.mcp?.stdio?.command).not.toMatch(/^npm|^npx/);
    expect(packageJson.scripts?.["start:stdio"]).toBeUndefined();
    expect(packageJson.mcp?.stdio?.command).toBe("node");
    expect(packageJson.mcp?.stdio?.args).toEqual([
      "./node_modules/tsx/dist/cli.mjs",
      "src/stdio.ts",
    ]);
  });

  it("does not write non-protocol logs to stdout from source entry", async () => {
    const source = await readFile(stdioEntryPath, "utf8");

    expect(source).not.toMatch(/console\.log\(/);
    expect(source).not.toMatch(/process\.stdout\.write\(/);
  });
});