Correctly closing Polka server when testing it with Jest and Supertest

Question

I have the following Jest test that runs against a Polka server:

import polka, {Polka} from 'polka';
import { agent as request } from 'supertest';


function brokenMiddleware(req, res, next) {
  throw new Error("foobar");
}


describe('integreration', () => {
  describe('middleware', () => {

    let testPolka: Polka;

    beforeEach(() => {
      testPolka = polka()
          .use(brokenMiddleware)
          .get('/', async (req, res) => {
            res.end('Hello world');
          });

    });

    afterEach(() => {
      if(testPolka) {
        if(testPolka.server) {
          testPolka.server.close()
        }
      }
    });

    it('should return active request', async () => {

      // Get active requests from the tracker
      const response = await request(testPolka.handler)
        .get('/')
        .set('Accept', 'application/json');

      await expect(response.headers["Content-Type"]).toMatch(/json/);
      await expect(response.status).toEqual(200);

    });

  });
});

Because the middleware is broken, jest never correctly exists.

If you run:

npx jest --detectOpenHandles test/polka.spec.ts

You will get:

Jest has detected the following 1 open handle potentially keeping Jest from exiting:

  ●  TCPSERVERWRAP

      34 |       // Get active requests from the tracker
      35 |       const response = await request(testPolka.handler)
    > 36 |         .get('/')
         |          ^
      37 |         .set('Accept', 'application/json');
      38 |
      39 |       await expect(response.headers["Content-Type"]).toMatch(/json/);

      at Test.serverAddress (node_modules/supertest/lib/test.js:48:35)
      at new Test (node_modules/supertest/lib/test.js:34:14)
      at TestAgent.<computed> [as get] (node_modules/supertest/lib/agent.js:47:17)
      at test/polka.spec.ts:36:10
      at test/polka.spec.ts:8:71
      at Object.<anonymous>.__awaiter (test/polka.spec.ts:4:12)
      at Object.<anonymous> (test/polka.spec.ts:32:51)
      at TestScheduler.scheduleTests (node_modules/@jest/core/build/TestScheduler.js:333:13)
      at runJest (node_modules/@jest/core/build/runJest.js:387:19)
      at _run10000 (node_modules/@jest/core/build/cli/index.js:408:7)
      at runCLI (node_modules/@jest/core/build/cli/index.js:261:3)

What would be the correct way to write Polka middleware and Jest tests so that

• Jest tests exit cleanly even if middleware is not functioning correctly

• Broken middleware does not cause issues for Polka in production

Answer 1

1. remove --detectOpenHandles, run npx jest test/polka.spec.ts.

    it('should return active request', () => {
      return request(testPolka.handler)
        .get('/')
        .set('Accept', 'application/json')
        .expect("Content-Type", /json/)
        .expect(200);
    });