Coveralls test percentage reduced by _typeof function

I've got an NPM package that uses Coveralls. My percentage is at 85% and I can see that the last 15% has to do with the following func:

function _typeof(obj) {
  if (typeof Symbol === "function" && typeof Symbol.iterator === "symbol") {
    _typeof = function (obj) {
      return typeof obj;
    };
  } else {
    _typeof = function (obj) {
      return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj;
    };
  }

  return _typeof(obj);
}

I assume this func is generated by Rollup because it is not in my src file.

Do I have to write tests for 'generated' code I haven't written my self? or is there some way to ignore this func.

from Coveralls test percentage reduced by _typeof function