Escape character not updated when switching database driver

[tenzap]

I have a test that uses a phpunit dataprovider having 3 values, each being the database driver to use. The 3 engines are PostgreSQL, MySQL, and sqlite.

It appears that when the test is run with 2nd case, MySQL, the escape char used to build the queries it's not updated to the one for MySQL which is `. It still is the one of PostgreSQL wich is ".

The cause is in this line of ci3.
https://github.com/bcit-ci/CodeIgniter/blob/3.1.13/system/database/DB_driver.php#L1417
If I remove the static from the $preg_ec variable, the escape char is correctly set for MySQL.