Testing Strategy

const user = userEvent.setup();
render(<LoginForm onSubmit={onSubmit} />);
await user.type(screen.getByLabelText(/email/i), "a@b.com");
await user.click(screen.getByRole("button", { name: /sign in/i }));
expect(onSubmit).toHaveBeenCalledWith({ email: "a@b.com" });

import request from "supertest";
import { app } from "../src/app";

it("rejects an order without items", async () => {
  const res = await request(app)
    .post("/orders")
    .set("Authorization", `Bearer ${await tokenFor({ tenantId: "t1", role: "buyer" })}`)
    .send({ items: [] });
  expect(res.status).toBe(400);
  expect(res.body.error.code).toBe("ORDER_EMPTY");
});

jest.mock("../src/db", () => ({
  query: jest.fn().mockResolvedValue({ rows: [{ id: 1, total: 100 }] }),
}));
import { query } from "../src/db";
import { getOrdersForTenant } from "../src/orders";

it("returns orders for tenant", async () => {
  const orders = await getOrdersForTenant("t1");
  expect(query).toHaveBeenCalled();
  expect(orders).toHaveLength(1);
});

import { PostgreSqlContainer, StartedPostgreSqlContainer } from "@testcontainers/postgresql";

let pg: StartedPostgreSqlContainer;
beforeAll(async () => {
  pg = await new PostgreSqlContainer("postgres:16-alpine").start();
  process.env.DATABASE_URL = pg.getConnectionUri();
  await runMigrations(process.env.DATABASE_URL);
}, 60_000);
afterAll(() => pg.stop());

it("shows search results", async () => {
  render(<ProductSearch />);
  fireEvent.change(screen.getByRole("searchbox"), { target: { value: "shoe" } });
  await new Promise((r) => setTimeout(r, 500)); // wait for debounce + fetch
  expect(screen.getByText("Running Shoe")).toBeInTheDocument();
});

it.each([
  ["buyer", "GET", "/admin/tenants", 403],
  ["merchant_admin", "GET", "/admin/tenants", 403],
  ["platform_admin", "GET", "/admin/tenants", 200],
])("%s %s %s -> %i", async (role, method, path, status) => {
  const token = await tokenFor({ role, tenantId: "t1" });
  const res = await request(app)[method.toLowerCase() as "get"](path).set("Authorization", `Bearer ${token}`);
  expect(res.status).toBe(status);
});

import { app } from "../src/app";
import { cache } from "../src/cache"; // module-level Map

describe("GET /products/:id", () => {
  it("returns 404 for unknown product", async () => {
    const res = await request(app).get("/products/999");
    expect(res.status).toBe(404);
  });
});

// another file, runs earlier in the same worker:
it("caches product 999 after creating it", async () => {
  await request(app).post("/products").send({ id: 999, name: "Tmp" });
  await request(app).get("/products/999");
  expect(cache.has("product:999")).toBe(true);
});

it("stores the order when OrderPlaced is consumed", async () => {
  await producer.send({ topic: "orders", messages: [{ value: JSON.stringify(event) }] });
  setTimeout(async () => {
    const row = await db.query("SELECT * FROM orders WHERE id = $1", [event.id]);
    expect(row.rows).toHaveLength(1);
  }, 2000);
});