Question

I’ve got a set of modules that run based on a global event emitter. They run based on a chronological chain of events, like so:

1. boot.ready
2. server created (because of boot.ready event)
3. server configured (because of server.created event)

As such, I need to create a server-test.js that performs tests in a chronological order.

Is this possible with Mocha? Something like the following?

var EventEmitter2      = require('eventemitter2').EventEmitter2,
    should             = require('should');

describe('server', function() {

    var mediator = new EventEmitter2({
            wildcard: false
        });

    require('../../src/routines/server/creator')(mediator);
    require('../../src/routines/server/configurer')(mediator);

    it('should be created after boot', function(done) {
        mediator.once('server.created', function(server) {
            server.should.exist;
            done();
        });

        it('should be configured after created', function(done) {
            mediator.once('server.configured', function() {
                done();
            });
        });

        mediator.emit('boot.ready');
    });
});

Because there seemed to be some confusion about the way this global event emitter works, this is the server/creator.js module:

module.exports = function(mediator) {

    var express = require('express');

    mediator.once('boot.ready', function() {

        var server = express.createServer();

        //event: server created
        mediator.emit('server.created', server);

    });
};

As you can see, the server is created after boot.ready. This fires server.created, after which the configurer will run which will then fire server.configured.

This chain of events needs to be tested by mocha.

Answer 1

If I’m testing a chain of events the quick way is to do it is nested eventEmitter.once calls like this:

it('executes in the right sequence', function(done) {
  mediator.once('boot.ready', function() {
    mediator.once('server.created', function() {
      done()
    })
  })
})

edit: as pointed out server.created will be fired before the test’s boot.ready handler is fired. Here’s a workaround:

it('executes in the right sequence', function(done) {
  var bootReadyFired = false
  mediator.once('boot.ready', function() {
    bootReadyFired = true
  })
  mediator.once('server.created', function() {
    assert.ok(bootReadyFired)
    done()
  })
})

Hope this helps.