You can test the different kinds of errors. All errors messages now use the JFactory enqueued messages rather than a extra message field. Technically we now handle the case the server spits out an exception (error is true) although I don't know how this would happen.

Finally we now get errors specific to the db property failing being rendered. You can test the following things:

1. Enter an invalid DB prefix (add an invalid character like an exclamation mark) - you'll get the Check your DB credentials, db type, db name or hostname string for form validation failure as well as the specific db prefix string (I've restored the Joomla 3 one which seemed to have been deleted along the way despite it's being used in 3 different places)

2. Enter an invalid password. The error message will show up with a more specific error than currently

e.g.

Could not connect to the database. Connector returned number: Could not connect to MySQL: Access denied for user 'root'@'localhost' (using password: YES)

(yes the message is kinda grim reading but this is the INSTL_DATABASE_COULD_NOT_CONNECT string - this can be refined in the future for sure :)

3. Obviously test the happy installer path continues to work