Use a function to mock new operator

newFunc.js

/**
 * Mock new operator.
 * Worked just as new operator.
 * @param {Function} Type
 * @param {...*} opt_args
 * @return {*}
 */
var newFunc = function(Type, opt_args) {
  var Ctor, proto;
  Ctor = function(){};
  Ctor.prototype = Type.prototype;
  proto = new Ctor();
  return Type.apply(proto, Array.prototype.slice.call(arguments, 1)) || proto;
};

newFunc_test.js

describe('newFunc', function() {
  it('should act as new operator', function() {
    var Ctor = function(value){ this.key = value; };
    var value = 'test-value';
    var obj = qd.newFunc(Ctor, value);
    expect(obj instanceof Ctor).toEqual(true);
    expect(obj.key).toEqual(value);
  });
});