code: function AssertionError (options) {
    options = options || {};
    this.message = options.message;
    this.actual = options.actual;
    this.expected = options.expected;
    this.operator = options.operator;
    this.showDiff = options.showDiff;
  
    if (options.stackStartFunction && Error.captureStackTrace) {
      var stackStartFunction = options.stackStartFunction;
      Error.captureStackTrace(this, stackStartFunction);
    }
  }
docs: # AssertionError (constructor)
  
  Create a new assertion error based on the Javascript
  `Error` prototype.
  
  **Options**
  - message
  - actual
  - expected
  - operator
  - startStackFunction
  
  @param {Object} options
  @api public