Automated Testing for Routes and Services

Required tools

• Node.js (20.x or 22.x LTS)
• npm (10.x (bundled with Node.js))

Setup

1. Reuse the `learning-api` project from earlier in this course.
2. Run `npm install --save-dev vitest supertest`.
3. Add `"test": "vitest run"` to the `scripts` section of package.json.
4. Add the files below, then run `npm test`.

Project structure

learning-api/
  src/
    server.js
    errors.js
    services/
      enrollments.service.js (new)
    routes/
      courses.routes.js
      enrollments.routes.js (updated: uses the service)
  tests/
    enrollments.service.test.js (new)
    enrollments.routes.test.js (new)

Starter files

export function createEnrollment(existingEnrollments, courseId, learnerId) {
  const alreadyEnrolled = existingEnrollments.some(
    (e) => e.courseId === courseId && e.learnerId === learnerId,
  );
  if (alreadyEnrolled) {
    throw new Error("Already enrolled in this course");
  }
  return { id: existingEnrollments.length + 1, courseId, learnerId, status: "active" };
}

import { describe, it, expect } from "vitest";
import { createEnrollment } from "../src/services/enrollments.service.js";

describe("createEnrollment", () => {
  it("creates a new enrollment with active status", () => {
    // TODO: setup fresh state, act, assert -- following this lesson's pattern
  });

  it("rejects a duplicate enrollment for the same course and learner", () => {
    // TODO
  });
});

import { describe, it, expect } from "vitest";
// TODO: import supertest and your Express app (you may need to export
// "app" from server.js separately from the app.listen() call so tests
// can import it without actually starting a real server).

describe("POST /enrollments", () => {
  it("returns 201 and the created enrollment for a valid request", async () => {
    // TODO
  });

  it("returns 400 for an invalid request", async () => {
    // TODO
  });
});

Requirements

• The enrollment-creation logic lives in a plain, testable service function with no req/res dependency
• At least two isolated service-level tests exist: one for successful creation, one for the duplicate-rejection case
• At least two HTTP-level tests exist using supertest: one for a valid POST (expects 201), one for an invalid POST (expects 400)
• `npm test` runs the full suite successfully with zero failures
• The server implements graceful shutdown: on SIGTERM, it stops accepting new connections and exits cleanly rather than terminating abruptly

Commands to run

• Run the test suite

  npm test

Expected behavior

Running npm test executes all four tests (two service-level, two HTTP-level) and reports them all passing, with no server left running afterward and no port conflicts on repeated runs.

Verify it yourself

• npm test

  Expected: All tests pass; the test process exits cleanly (does not hang)

• Run the server, then send it a SIGTERM (Ctrl+C in most terminals sends SIGINT, which behaves similarly for this purpose)

  Expected: The server logs a shutdown message and exits, rather than terminating instantly mid-request

Troubleshooting

• supertest tests hang and never complete — Confirm server.js exports the Express `app` object separately from calling app.listen() — tests should import and use the app directly with supertest, which manages its own ephemeral server, rather than connecting to a real running instance.
• npm test fails with 'vitest: command not found' — Confirm vitest was installed as a devDependency (npm install --save-dev vitest) and that the test script in package.json matches exactly.

Extension challenge

Add a test confirming that two DIFFERENT learners can both enroll in the SAME course without triggering the duplicate-rejection guard, exercising the boundary of what counts as a 'duplicate.'