text: SELECT COUNT(@@GLOBAL.innodb_undo_directory);
  COUNT(@@GLOBAL.innodb_undo_directory)
  1
  1 Expected
  SET @@GLOBAL.innodb_undo_directory="/tmp";
  ERROR HY000: Variable 'innodb_undo_directory' is a read only variable
  Expected error 'Read only variable'
  SELECT COUNT(@@GLOBAL.innodb_undo_directory);
  COUNT(@@GLOBAL.innodb_undo_directory)
  1
  1 Expected
  SELECT @@GLOBAL.innodb_undo_directory = VARIABLE_VALUE
  FROM performance_schema.global_variables
  WHERE VARIABLE_NAME='innodb_undo_directory';
  @@GLOBAL.innodb_undo_directory = VARIABLE_VALUE
  1
  1 Expected
  SELECT COUNT(@@GLOBAL.innodb_undo_directory);
  COUNT(@@GLOBAL.innodb_undo_directory)
  1
  1 Expected
  SELECT COUNT(VARIABLE_VALUE)
  FROM performance_schema.global_variables 
  WHERE VARIABLE_NAME='innodb_undo_directory';
  COUNT(VARIABLE_VALUE)
  1
  1 Expected
  SELECT @@innodb_undo_directory = @@GLOBAL.innodb_undo_directory;
  @@innodb_undo_directory = @@GLOBAL.innodb_undo_directory
  1
  1 Expected
  SELECT COUNT(@@innodb_undo_directory);
  COUNT(@@innodb_undo_directory)
  1
  1 Expected
  SELECT COUNT(@@local.innodb_undo_directory);
  ERROR HY000: Variable 'innodb_undo_directory' is a GLOBAL variable
  Expected error 'Variable is a GLOBAL variable'
  SELECT COUNT(@@SESSION.innodb_undo_directory);
  ERROR HY000: Variable 'innodb_undo_directory' is a GLOBAL variable
  Expected error 'Variable is a GLOBAL variable'
  SELECT COUNT(@@GLOBAL.innodb_undo_directory);
  COUNT(@@GLOBAL.innodb_undo_directory)
  1
  1 Expected
  SELECT innodb_undo_directory = @@SESSION.innodb_undo_directory;
  ERROR 42S22: Unknown column 'innodb_undo_directory' in 'field list'
  Expected error 'Readonly variable'
  