code: func (c *clientIdentityImpl) AssertAttributeValue(attrName, attrValue string) error {
  	val, ok, err := c.GetAttributeValue(attrName)
  	if err != nil {
  		return err
  	}
  	if !ok {
  		return errors.Errorf("Attribute '%s' was not found", attrName)
  	}
  	if val != attrValue {
  		return errors.Errorf("Attribute '%s' equals '%s', not '%s'", attrName, val, attrValue)
  	}
  	return nil
  }
docs: // AssertAttributeValue checks to see if an attribute value equals the specified value