unreal-engine-mcp-system-plugin/test/server.test.js

// End-to-end smoke: spawn the MCP server as a subprocess, speak the wire
// protocol over stdio, verify tools/list and a dry_run apply_graph.
import { test } from "node:test";
import assert from "node:assert/strict";
import { spawn } from "node:child_process";
import path from "node:path";
import { fileURLToPath } from "node:url";

const HERE = path.dirname(fileURLToPath(import.meta.url));
const SERVER = path.resolve(HERE, "..", "src", "server.js");

function startServer() {
  const proc = spawn(process.execPath, [SERVER], { stdio: ["pipe", "pipe", "pipe"] });
  let buf = "";
  const pending = new Map();
  let nextId = 1;
  proc.stdout.on("data", chunk => {
    buf += chunk.toString();
    let idx;
    while ((idx = buf.indexOf("\n")) >= 0) {
      const line = buf.slice(0, idx); buf = buf.slice(idx + 1);
      if (!line.trim()) continue;
      try {
        const msg = JSON.parse(line);
        if (msg.id && pending.has(msg.id)) {
          const { resolve } = pending.get(msg.id);
          pending.delete(msg.id);
          resolve(msg);
        }
      } catch { /* ignore non-JSON banner */ }
    }
  });
  proc.stderr.on("data", () => { /* swallow */ });

  function send(method, params) {
    const id = nextId++;
    const msg = { jsonrpc: "2.0", id, method, params };
    return new Promise((resolve, reject) => {
      pending.set(id, { resolve, reject });
      proc.stdin.write(JSON.stringify(msg) + "\n");
      setTimeout(() => {
        if (pending.has(id)) { pending.delete(id); reject(new Error(`timeout: ${method}`)); }
      }, 5000);
    });
  }
  function close() { try { proc.kill(); } catch {} }
  return { send, close };
}

async function initialize(send) {
  return send("initialize", {
    protocolVersion: "2024-11-05",
    capabilities: {},
    clientInfo: { name: "test", version: "0" },
  });
}

test("MCP server lists tools over stdio", async () => {
  const { send, close } = startServer();
  try {
    await initialize(send);
    const r = await send("tools/list", {});
    const names = r.result.tools.map(t => t.name);
    assert.ok(names.includes("apply_graph"));
    assert.ok(names.includes("introspect"));
    assert.ok(names.includes("compile"));
    assert.ok(names.includes("read_graph"));
    assert.ok(names.includes("ping_ue"));
    assert.ok(names.includes("selection_op"));
    assert.ok(names.includes("voxel_graph_op"));
    assert.ok(names.includes("material_op"));
  } finally { close(); }
});

test("apply_graph dry_run returns python without calling UE", async () => {
  const { send, close } = startServer();
  try {
    await initialize(send);
    const r = await send("tools/call", {
      name: "apply_graph",
      arguments: {
        bp_path: "/Game/Test/BP_Foo",
        nodes: [
          { id: "ev", kind: "event", target: "BeginPlay", position: [0, 0] },
          { id: "br", kind: "branch", position: [400, 0] },
        ],
        edges: [{ from: ["ev", "Then"], to: ["br", "Exec"] }],
        dry_run: true,
      },
    });
    assert.equal(r.result.isError ?? false, false);
    const payload = JSON.parse(r.result.content[0].text);
    assert.equal(payload.dry_run, true);
    assert.match(payload.python, /apply_graph\.entrypoint/);
    assert.match(payload.python, /BeginPlay/);
  } finally { close(); }
});

test("apply_graph rejects invalid graphs", async () => {
  const { send, close } = startServer();
  try {
    await initialize(send);
    const r = await send("tools/call", {
      name: "apply_graph",
      arguments: { bp_path: "not-a-game-path", nodes: [] },
    });
    assert.equal(r.result.isError, true);
    assert.match(r.result.content[0].text, /bp_path/);
  } finally { close(); }
});