Test cases:

• group by one field (group by m2o, selection, integer, m2m, date, ...)
• group by multiple fields
• group by 0 field: back to default group by
• create a new record
• drag and drop record to update
• click on the group by to view the group by record detail
• when group by m2m field, record is displayed multiple times if linked to multiple m2m records
• when drag and drop, the value of the m2m field should not be updated as there is no best way to handle this
• when creating a new record, set the default value for all grouped fields
• handle group by non-relation fields: click on the group of selection or char field do not popup record form view to avoid error.
• dependency_arrow between multiple collapse/expand groups