1) Create a custom field as Alphanumeric, CheckBox, Options Per Line = 1, with several options.
2) Add this field to a CiviCRM profile as Searchable.
3) Visit <site root>/civicrm/profile?reset=1&gid=N (where N is the Profile ID).
Profile search form displays the checkboxes for the custom field all on one line, wrapped at will by the browser.
Profile search form should display the checkboxes for the custom field as specified by the Options Per Line parameter, in this case one per line.