mqtt.connect giving error in Jest: Jest has detected the following 1 open handle potentially keeping Jest from exiting

[anthonyma94]

I have a test for a class that revolves around MQTT:

MQTTHMIPlugin.ts

export class MQTTHMIPlugin {
    private clients: MqttClient[];

    // Specifically not using a constructor for DI reasons
    init() {
        if (!process.env.MQTT_URL) {
            throw new Error("Missing MQTT_URL environment variable.");
        }
        const urls = process.env.MQTT_URL.split(/,\s*/);

        this.clients = [];

        for (const url of urls) {
            const client = mqtt.connect(url);
            client.on("connect", () => {
                logger.info(`MQTT client connected to ${url}`);
            });
            this.clients.push(client);
        }
    }
    cleanup() {
        for (const client of this.clients) {
            if (client.connected) {
                client.end();
            }
        }
    }
   ...
}

MQTTHMIPlugin.spec.ts

describe("MQTT HMI Plugin tests", () => {
    let plugin: MQTTHMIPlugin;
    let aedes: ReturnType<typeof Aedes>;  // in-memory MQTT server
    let server: net.Server;  // in-memory MQTT server

    beforeAll(() => {
        process.env.MQTT_URL = "mqtt://localhost:1883";
        aedes = Aedes();
        server = net.createServer(aedes.handle);
        server.listen(1883, function () {
            // console.log(`MQTT server started on port 1883.`);
        });
    });

    beforeEach(() => {
        if (plugin) {
            plugin.cleanup();
        }
        plugin = new MQTTHMIPlugin();
    });

    afterAll((done) => {
        plugin.cleanup();
        aedes.close(() => {
            server.close();
        });
        done();
    });

    test("init function", (done) => {
        plugin.init();
        console.log(aedes.connectedClients);
        expect(0).toBe(0);
        plugin.cleanup();
        done();
    });
});

Even though I'm calling cleanup() in 3 different places and calling done, Jest still thinks there's an open handle and refuses to exit:

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

  ●  Timeout

      23 |
      24 |         for (const url of urls) {
    > 25 |             const client = mqtt.connect(url);
         |                                 ^
      26 |             client.on("connect", () => {
      27 |                 logger.info(`MQTT client connected to ${url}`);
      28 |             });

How can I have Jest exit properly, without using --forceExit?

[FreTimmerman]

i had the same problem. this issue got me thinking and i tried something.

i got a successful close of the mqtt client by adding a waiting period (mine was 3 seconds)

export const mqttShutdown = () => {
  return new Promise<void>((resolve) =>
    client.end(true, {}, () => {
      setTimeout(() => {
        resolve();
      }, 3000);
    }),
  );
};

so i guess in your case that will become: (below code is untested, just quickly written to try to translate my approach to your callback-based and multi-client approach)

cleanup(doneCallback) {
  Promise.all(
    this.clients.map((client) => {
      return new Promise((resolve) => {
        if (client.connected) {
          client.end(true, {}, () => {
            setTimeout(resolve, 3000);
          });
        } else {
          resolve();
        }
      });
    });
  )
  .then(() => {
    doneCallback();
  });
}

and then use

plugin.cleanup(done)

do note that i added true to the client.end(), in order to force it closed. i found that this speeds up the closing.

and since by default you can't have more than 5s for a hook in jest this is useful...

[sibelius]

is this for integration tests?

[sibelius]

can you provide a sample test with jest?

[robertsLando]

Anyone that would like to try mqtt@beta to see if this error is gone now?

[sibelius]

does it make sense to expose mqttserver for testing purposes? and add some guides of how to test with jest?

https://github.com/mqttjs/MQTT.js/blob/main/test/server_helpers_for_client_tests.js
https://github.com/mqttjs/MQTT.js/blob/main/test/server.js

[robertsLando]

Follow: #1641

[robertsLando]

MQTT 5.0.0 BETA is now available! Try it out and give us feedback: npm i mqtt@beta. It may fix your issues