test: Fix EventEmitter.MaxListenersExceededWarning warning

[sudo-suhas]

Summary

When tests are run, node logs warnings - MaxListenersExceededWarning: Possible EventEmitter memory leak detected. This fixes thewarning by setting the max listeners to 20 on process(EventEmitter)

Details

When running tests, the following warnings are logged:

(node:10188) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGTERM listeners added. Use emitter.setMaxListeners() to increase limit
(node:10188) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGINT listeners added. Use emitter.setMaxListeners() to increase limit
(node:10188) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGBREAK listeners added. Use emitter.setMaxListeners() to increase limit
(node:10188) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGHUP listeners added. Use emitter.setMaxListeners() to increase limit

The warning can be seen in the travis build logs as well as appveyor.

I used the following code to print the warning stack trace:

process.on('warning', warning => {
  console.log(warning.name)
  console.log(warning.message)
  console.log(warning.stack)
})

Warnings stack trace

 PASS  src\index.test.js
  ● Console

    console.log src\index.test.js:6
      MaxListenersExceededWarning
    console.log src\index.test.js:7
      Possible EventEmitter memory leak detected. 11 SIGTERM listeners added. Use emitter.setMaxListeners() to increase limit
    console.log src\index.test.js:8
      MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGTERM listeners added. Use emitter.setMaxListeners() to increase limit
          at _addListener (events.js:281:19)
          at process.addListener (events.js:298:10)
          at crossEnv (E:\Projects\repos\cross-env\src\index.js:21:13)
          at Object.<anonymous> (E:\Projects\repos\cross-env\src\index.test.js:65:3)
          at Object.<anonymous> (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:42:32)
          at attemptAsync (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1984:24)
          at QueueRunner.run (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1939:9)
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1966:16
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1909:9
          at Object.fn (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:68:11)
    console.log src\index.test.js:6
      MaxListenersExceededWarning
    console.log src\index.test.js:7
      Possible EventEmitter memory leak detected. 11 SIGINT listeners added. Use emitter.setMaxListeners() to increase limit
    console.log src\index.test.js:8
      MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGINT listeners added. Use emitter.setMaxListeners() to increase limit
          at _addListener (events.js:281:19)
          at process.addListener (events.js:298:10)
          at crossEnv (E:\Projects\repos\cross-env\src\index.js:22:13)
          at Object.<anonymous> (E:\Projects\repos\cross-env\src\index.test.js:65:3)
          at Object.<anonymous> (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:42:32)
          at attemptAsync (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1984:24)
          at QueueRunner.run (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1939:9)
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1966:16
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1909:9
          at Object.fn (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:68:11)
    console.log src\index.test.js:6
      MaxListenersExceededWarning
    console.log src\index.test.js:7
      Possible EventEmitter memory leak detected. 11 SIGBREAK listeners added. Use emitter.setMaxListeners() to increase limit
    console.log src\index.test.js:8
      MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGBREAK listeners added. Use emitter.setMaxListeners() to increase limit
          at _addListener (events.js:281:19)
          at process.addListener (events.js:298:10)
          at crossEnv (E:\Projects\repos\cross-env\src\index.js:23:13)
          at Object.<anonymous> (E:\Projects\repos\cross-env\src\index.test.js:65:3)
          at Object.<anonymous> (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:42:32)
          at attemptAsync (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1984:24)
          at QueueRunner.run (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1939:9)
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1966:16
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1909:9
          at Object.fn (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:68:11)
    console.log src\index.test.js:6
      MaxListenersExceededWarning
    console.log src\index.test.js:7
      Possible EventEmitter memory leak detected. 11 SIGHUP listeners added. Use emitter.setMaxListeners() to increase limit
    console.log src\index.test.js:8
      MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 SIGHUP listeners added. Use emitter.setMaxListeners() to increase limit
          at _addListener (events.js:281:19)
          at process.addListener (events.js:298:10)
          at crossEnv (E:\Projects\repos\cross-env\src\index.js:24:13)
          at Object.<anonymous> (E:\Projects\repos\cross-env\src\index.test.js:65:3)
          at Object.<anonymous> (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:42:32)
          at attemptAsync (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1984:24)
          at QueueRunner.run (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1939:9)
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1966:16
          at E:\Projects\repos\cross-env\node_modules\jest-jasmine2\vendor\jasmine-2.5.2.js:1909:9
          at Object.fn (E:\Projects\repos\cross-env\node_modules\jest-jasmine2\build\jasmine-async.js:68:11)

As can be seen, the warnings originate from src/index.js#L21-L24. Fixed by increasing max listeners.

[codecov]

Codecov Report

Merging #132 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #132   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           3      3           
  Lines          50     50           
=====================================
  Hits           50     50

---

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[kentcdodds]

Thanks for this! I've noticed this also and didn't realize it could be fixed with cross-env! But is it really cross-env? Seems like this is actually a problem with whatever process you're trying to spawn. I'm not sure that this is the right place to fix the problem... 🤔

[sudo-suhas]

During tests, cross-env is invoked multiple times. So they all end up adding listeners to process. Node has a default limit of 10 and that causes the warning. Note that this is only possible if you are invoking cross-env from js. If you were using the command line, each invocation would have it's own process.

Edit:
These are all the locations the cross-env function, which adds listeners on process, is invoked:

• src/index.test.js#L59
• src/index.test.js#L75
• src/index.test.js#L101

[kentcdodds]

Ah! I see, I thought this change was inside cross-env source code to fix an issue you were seeing in another project. But now I see it's in the cross-env tests. Thank you for the fix 😄