backbone-requirer.js

var Backbone = require('backbone');

gulpfile.js

var gulp = require('gulp');
var mocha = require('gulp-mocha');
var backboneRequirer = require('./backbone-requirer');

gulp.task('mocha', function() {
  return gulp.src('./node.js')
    .pipe(mocha());
});

loaded-by-gulp.js

var $ = require('jquery');
console.log('this is undefined:');
console.log($.Deferred);

package.json

{
  "devDependencies": {
    "gulp": "^3.9.0",
    "gulp-mocha": "^2.1.1",
    "gulp-plumber": "^1.0.1"
  },
  "dependencies": {
    "backbone": "^1.2.1",
    "jquery": "^2.1.4"
  }
}