setTimeout() after done() is called (--watch mode)

[gabssnake]

Hello, thanks for your work on this project.

The following test passes when calling mocha from cli, but the assertion throws after the test passes when adding the --watch flag.

Changing setTimeout to process.nextTick makes the test always pass in both modes.
Changing the delay on setTimeout to lower values (10ms) makes the test pass sometimes in watch mode.

What is the expected behaviour?

var assert = require('assert');

describe('Works consistently in regular cli and watch mode', function() {
  it('ignores setTimeout after done is called', function(done) {
    function myFunc(callback) {
      callback('sync');
      setTimeout(function() { callback('async'); }, 100);
    }

    myFunc(function(data) {
      assert.equal(data, 'sync');
      done();
    });
  });
});

Kind regards,

mocha 3.5.3
node 6.11.2
macOS 10.12.6

[ScottFreeCode]

Calling done multiple times is an error, as the first done call is supposed to indicate to Mocha that the test is complete. It's possible for the second done call to never execute because Mocha shuts down too quickly before it can, especially if it's the last asynchronous test; --no-exit should prevent that, and I'd imagine --watch prevents it as a side effect as well. Not so sure about anything being changed by nextTick or a shorter timeout -- those should make the error more likely to be shown since the second done call occurs faster, but I'll play around with this a little and see if I discover anything. We do have issue #2879 for changing the default behavior to not shut down if there's anything still running and instead have --exit to get the old default behavior, although it'll have to wait for a semver "major" update.

[gabssnake]

Thanks for your answer.

Please see/try the following test case.

With --no-exit flag, test passes, it takes 10 secs to exit, no assertion is thrown.

With --watch flag, test passes, it takes 10 secs to throw: AssertionError: 'async3' == 'sync'. nextTick and shorter setTimeout never throw.

What is happening?

it('passes, then throws after 10 secs but only in --watch', function(done) {
  function myFunc(callback) {
    callback('sync');
    process.nextTick(function() { callback('async1'); });
    setTimeout(function() { callback('async2'); }, 0);
    setTimeout(function() { callback('async3'); }, 10000);
  }
  myFunc(function(data) {
    assert.equal(data, 'sync');
    done();
  });
});

[boneskull]

good question.

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[gabssnake]

Time travelers: This issue has been resolved since mocha v4, released Sep 28, 2017.

The behavior is now consistent (always throws) in normal and watch mode, both with and without the --exit flag. Yay for consistency!

Thanks for the good work @boneskull and everyone!