mocha-generators.md

Using mocha-generators

mocha-generators can be used for flow control while testing under mocha. This allows yield to be used during testing, as well as grants the ability to use generators for before, beforeEach, after, and afterEach. Currently, it is what Nightmare uses for unit testing.

Consider the following vanilla mocha test, which determines existence or nonexistence of elements:

var should = require('chai').should();
var Nightmare = require('nightmare');
var server = require('./server');

describe('Nightmare', function() {
  var nightmare;
  //before all of the tests,
  before(function(done) {
    //have the test server listen on a given port
    server.listen(7500, done);
  });

  //before each test,
  beforeEach(function(){
    //create a new nightmare instance
    nightmare = Nightmare();
  });
  
  //after each test,
  afterEach(function(done){ 
    //end the nightmare instance
    nightmare.end(done);
  })

  it('should check if the selector exists', function(done) {
    nightmare
      //go to the test url
      .goto('http://localhost:7500')
      //determine if the header with the title class exists
      .exists('h1.title')
      //execute the chain
      .then((exists) => {
        //assert existence
        exists.should.be.true;
      })
      .then(() => {
        //return a nightmare-thennable to check if an anchor with the blahblahblah class exists
        return nightmare.exists('a.blahblahblah')
      })
      .then((exists) => {
        //assert nonexistence
        exists.should.be.false;
      })
      //done
      .then(() => done());
  });
});

The above could be rewritten using generators for readability:

require('mocha-generators').install();
var should = require('chai').should();
var Nightmare = require('nightmare');
var server = require('./server');

describe('Nightmare', function() {
  var nightmare;
  //before all of the tests,
  before(function(done) {
    //have the test server listen on a given port
    server.listen(7500, done);
  });

  //before each test,
  beforeEach(function(){
    //create a new nightmare instance
    nightmare = Nightmare();
  });
  
  //after each test,
  afterEach(function *(){ 
    //end the nightmare instance
    yield nightmare.end();
  })

  it('should check if the selector exists', function * () {
    //yield on the chain of actions that follows
    var exists = yield nightmare
      //go to the test url
      .goto('http://localhost:7500')
      //determine if the header with the title class exists
      .exists('h1.title');

    exists.should.be.true;

    //again, yield on the chain of actions that follow
    exists = yield nightmare
      //determine if there is an anchor with the blahblahblah class
      .exists('a.blahblahblah');

    exists.should.be.false;
  });
});

References

• Runnable mocha-generator examples - note you will need mocha installed
• mocha
• MDN function* documentation
• MDN yield documentation
• Nightmare tests