nEngine/apps/mcp-server/test/roundtrip.test.ts

import { resolve } from "node:path";
import { describe, expect, it } from "vitest";
import { createEngine } from "@nengine/core";
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { InMemoryTransport } from "@modelcontextprotocol/sdk/inMemory.js";
import { createNengineMcpServer, createGateway } from "../src/server.js";

const repoRoot = resolve(process.cwd(), "../..");
const contentDir = resolve(repoRoot, "content");
const modsDir = resolve(repoRoot, "mods");

interface Roundtrip {
  engine: ReturnType<typeof createEngine>;
  server: ReturnType<typeof createNengineMcpServer>;
  client: Client;
  close: () => Promise<void>;
}

async function setup(gateway?: ReturnType<typeof createGateway>): Promise<Roundtrip> {
  const engine = createEngine({ contentDir, modsDir });
  await engine.start();
  const server = gateway ? createNengineMcpServer(engine, gateway) : createNengineMcpServer(engine);
  const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
  await server.connect(serverTransport);
  const client = new Client({ name: "roundtrip-test", version: "0.0.1" });
  await client.connect(clientTransport);
  return {
    engine,
    server,
    client,
    close: async () => {
      await client.close();
      await server.close();
      await engine.stop();
    },
  };
}

function textOf(result: { content: { type: string; text?: string }[] }): string {
  return result.content.find((block) => block.type === "text")?.text ?? "";
}

function contentsOf(result: { contents: { text?: string }[] }): string {
  return result.contents[0]?.text ?? "";
}

describe("apps/mcp-server SDK roundtrip (in-memory transport)", () => {
  it("initialize, listTools, callTool, resources, and prompts roundtrip", async () => {
    const { client, close } = await setup();
    try {
      const tools = await client.listTools();
      const toolNames = tools.tools.map((tool) => tool.name);
      expect(toolNames).toEqual(
        expect.arrayContaining([
          "server.info",
          "server.status",
          "map.list",
          "map.get",
          "time.get",
          "time.advance",
          "time.set",
        ]),
      );

      const result = await client.callTool({ name: "map.get", arguments: {} });
      expect(result.isError).toBeUndefined();
      const map = JSON.parse(textOf(result)) as { id: string; player: { x: number; y: number } };
      expect(map.id).toBe("farm");
      expect(map.player.x).toBe(2);

      const advanced = await client.callTool({ name: "time.advance", arguments: { ticks: 480 } });
      const time = JSON.parse(textOf(advanced)) as { day: number };
      expect(time.day).toBe(2);

      const resources = await client.listResources();
      expect(resources.resources.map((resource) => resource.uri)).toEqual(
        expect.arrayContaining(["server://status", "time://state", "map://{mapId}"]),
      );
      const state = await client.readResource({ uri: "time://state" });
      expect(JSON.parse(contentsOf(state))).toEqual({ day: 2, season: "spring", tickInDay: 0 });

      const prompts = await client.listPrompts();
      expect(prompts.prompts.map((prompt) => prompt.name)).toContain("server.orient");
      const orient = await client.getPrompt({ name: "server.orient", arguments: {} });
      expect(orient.messages[0]?.content).toMatchObject({ type: "text", text: expect.stringContaining("nEngine MCP server") });
    } finally {
      await close();
    }
  });

  it("disabled namespaces are absent from tools/list and fail on tools/call", async () => {
    const engine = createEngine({ contentDir, modsDir });
    await engine.start();
    const gateway = createGateway(engine);
    gateway.disable("time");
    const server = createNengineMcpServer(engine, gateway);
    const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
    await server.connect(serverTransport);
    const client = new Client({ name: "roundtrip-test", version: "0.0.1" });
    await client.connect(clientTransport);
    try {
      const tools = await client.listTools();
      expect(tools.tools.some((tool) => tool.name.startsWith("time."))).toBe(false);
      expect(tools.tools.some((tool) => tool.name === "map.get")).toBe(true);

      const rejected = await client.callTool({ name: "time.get", arguments: {} });
      expect(rejected.isError).toBe(true);
      expect(textOf(rejected)).toMatch(/namespace "time" is disabled/);
    } finally {
      await client.close();
      await server.close();
      await engine.stop();
    }
  });

  it("surfaces resource errors over the wire", async () => {
    const { client, close } = await setup();
    try {
      await expect(client.readResource({ uri: "map://does-not-exist" })).rejects.toThrow(/map not found/);
    } finally {
      await close();
    }
  });
});