function assertOptions(options, schema, allowUnknown) {
  if (typeof options !== 'object') {
    throw new AxiosError('options must be an object', AxiosError.ERR_BAD_OPTION_VALUE);
  }
  const keys = Object.keys(options);
  let i = keys.length;
  while (i-- > 0) {
    const opt = keys[i];
    const validator = schema[opt];
    if (validator) {
      const value = options[opt];
      const result = value === undefined || validator(value, opt, options);
      if (result !== true) {
        throw new AxiosError('option ' + opt + ' must be ' + result, AxiosError.ERR_BAD_OPTION_VALUE);
      }
      continue;
    }
    if (allowUnknown !== true) {
      throw new AxiosError('Unknown option ' + opt, AxiosError.ERR_BAD_OPTION);
    }
  }
}
Assert object's properties type

@param {object} options
@param {object} schema
@param {boolean?} allowUnknown

@returns {object}