How to stop Jest from hanging when testing WebSockets?

Question

I created an app in node.js which gives me a WebSocket interface using the 'ws' package from NPM on the server. Now I want to test this interface with Jest. The test runs successful but Jest does not exit and gives me the error:

Jest did not exit one second after the test run has completed.

I read the documentation and found that I have to use the done parameter in the test and call it when the test has finished.

The server will be started in the beforeAll function and stopped in the afterAll function given by Jest.

describe('app', () => {
    it('connect websockets response' (done), => {
        expect.assertions(1);

        new WebSocket(`ws://localhost:${port}`).on('message' (msg), => {
                expect(JSON.parse(msg).id).toEqual(0);
                done();
            })
    });
});

I expect that Jest stops successful after the test has finished.

score 20 · Accepted Answer · edited Aug 08 '20 at 20:32

20

I have learned that I have to close the WebSocket connection in the test itself, and wait for the closing event.

describe('app', () => {
    it('connect websockets response', (done) => {
        expect.assertions(1);

        const ws = new WebSocket(`ws://localhost:${port}`)
            .on('message', (msg) => {
                expect(JSON.parse(msg).id).toEqual(0);
                ws.close();
            })
            .on('close', () => done());
    });
});

edited Aug 08 '20 at 20:32

Timo Tijhof

10,032
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answered May 03 '19 at 05:11

FleMo

539
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20

do you have an example repro? – Sibelius Seraphini Oct 13 '20 at 17:59
@SibeliusSeraphini Sorry i don't have an example repo. It's all company code on private machines. Therefore i can't share more than this. What exactly do you need it for? Can i help you in other ways? – FleMo Oct 14 '20 at 05:10
I tried this solution *exact same structure and it just works. – fsevenm Dec 17 '20 at 21:28

score 2 · Answer 2 · answered May 31 '22 at 07:15

This is what worked for me using TypeScript

  test('connect websockets response', (done) => {
    const ws = new WebSocket(`ws://localhost:${port}`);

    const listener = (msg: MessageEvent) => {
      console.log(JSON.parse(msg.data));
      // Put you expect statement here
      ws.removeEventListener('message', listener);
      ws.close();
    };

    ws.addEventListener('message', listener);

    ws.addEventListener('close', () => done());
  }, 30000);

How to stop Jest from hanging when testing WebSockets?

2 Answers2