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