This commit fixes a bug in WC_Customer_Download_Log_Data_Store::get_download_logs() that made impossible to change the order in which the query returned the results. This method accepts the arguments order_by and order, but it was ignoring them and always using the default values ('download_log_id' and 'ASC' respectively).
It also introduces a very basic unit test to cover the method main functionality and to make sure that the parameters order and orderby are not ignored anymore.
It seems that the modified method was inspired in WC_Customer_Download_Data_Store::get_downloads() before the same bug was fixed in #18620.
Rodrigo Primo