mesh-tools/test/client.test.ts

/**
 * A person's client, against a real bus.
 *
 * What is worth checking is not that a request/reply works — the runtime's own tests cover that — but
 * that the two surfaces are the same thing. An agent and a person must see the same tools and get the
 * same answers, or the MCP surface becomes a second definition of what a tool is.
 *
 *   docker run -d --rm --name t -p 14232:4222 nats:2.10-alpine -js
 *   MESH_TEST_NATS=nats://127.0.0.1:14232 node --test --experimental-strip-types test/client.test.ts
 */
import assert from "node:assert/strict";
import { test } from "node:test";

// The built output, not the source: the client imports its siblings as `.js`, which is what ships and
// what every other file here does, and cannot be loaded as TypeScript directly. `pretest` builds.
import { connectNats } from "../dist/broker-nats.js";
import { callTool, toolsOn, whyItFailed } from "../dist/client.js";

const url = process.env.MESH_TEST_NATS;

/** A module serving the catalogue's tool list and one tool of its own, so the client has a mesh to
 *  talk to. Two connections, because a person and a module are different users even in a test. */
async function aMeshWithTools() {
  const catalogue = await connectNats({ url: url!, module: "mesh-catalog" });
  const shop = await connectNats({ url: url!, module: "shop" });
  await catalogue.handle("catalog_tools", async () => ({
    tools: [
      { module: "shop", name: "price", description: "what something costs", input: { type: "object" } },
      { module: "mesh-catalog", name: "catalog_tools", description: "what tools the mesh has" },
    ],
  }));
  await shop.handle("price", async (body: { of?: string }) => ({ of: body.of ?? "nothing", cost: 12 }));
  return {
    async close() {
      await catalogue.close();
      await shop.close();
    },
  };
}

test("a person sees what the catalogue says the mesh has, sorted", async (t) => {
  if (!url) return t.skip("MESH_TEST_NATS unset");
  const mesh = await aMeshWithTools();
  const person = await connectNats({ url, module: "person.ada" });
  try {
    const tools = await toolsOn(person);
    assert.deepEqual(
      tools.map((x) => `${x.module}.${x.name}`),
      ["mesh-catalog.catalog_tools", "shop.price"],
      "the list is what the catalogue answered, in a stable order",
    );
  } finally {
    await person.close();
    await mesh.close();
  }
});

test("a person calls a tool and gets the module's own answer, unshaped", async (t) => {
  if (!url) return t.skip("MESH_TEST_NATS unset");
  const mesh = await aMeshWithTools();
  const person = await connectNats({ url, module: "person.ada" });
  try {
    const answer = await callTool(person, "shop.price", { of: "a hat" });
    assert.deepEqual(answer, { of: "a hat", cost: 12 });
  } finally {
    await person.close();
    await mesh.close();
  }
});

test("a tool nobody serves says so at once, and says what to do about it", async (t) => {
  if (!url) return t.skip("MESH_TEST_NATS unset");
  const person = await connectNats({ url: url!, module: "person.ada" });
  try {
    const began = Date.now();
    await assert.rejects(() => callTool(person, "ghost.missing", {}));
    // At once, not after the whole wait: "that module is down" and "that tool is slow" need
    // different things done, and a timeout cannot tell them apart.
    assert.ok(Date.now() - began < 5_000, "a tool nobody serves waited out the timeout");
  } finally {
    await person.close();
  }
});

test("a name that is not <module>.<tool> is refused before anything is sent", async (t) => {
  if (!url) return t.skip("MESH_TEST_NATS unset");
  const person = await connectNats({ url: url!, module: "person.ada" });
  try {
    await assert.rejects(() => callTool(person, "price", {}), /does not name a tool/);
  } finally {
    await person.close();
  }
});

test("each way a call fails says what to do about it", () => {
  // The three answers a person actually gets. Without this they are one timeout and a stack trace,
  // and the remedies are in three different places.
  assert.match(whyItFailed("shop.price", new Error("no responders")), /nothing serves shop\.price/);
  assert.match(
    whyItFailed("shop.price", new Error("Permissions Violation for Publish")),
    /may not call shop\.price/,
  );
  assert.match(whyItFailed("shop.price", new Error("timeout")), /did not answer in time/);
  assert.match(whyItFailed("shop.price", new Error("something else")), /something else/);
});