Default setting of Rails

i have just installed RoR. when i create a new rails project use the
command "rails test" without any options, the default database setting
is sqlite3 in my computer. the default should be MySQL, is anything i
did wrong?

how do i fix it?

The new default is SQLite. This is a really recent change, so if
you're following nearly any book in print or an older online article,
it will say MySQL.

To change it, you can use the -d option.

   rails your_app -d mysql