- add test for isCompleted implementation

 - create commong mixin class for low level BPM tests and put common methods into, to avoid code repetition, left some repetition for better readability
 - refactor existing tests to use mixin class
 - use variable for completed state, use this variable


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28129 20353a03-c40f-0410-a6d1-a30d3c3de9de