fix tests and unskip them we should test the behaviour specified in the description of every test.

The puzzle `64-4a56c855` from #64 has to be resolved:

https://github.com/ammaratef45/Attendance/blob/9d172f640f3e4f0101e2e8d04f3d97ff0b165fe6/attendance/test/dialogs_test.dart#L20-L22

The puzzle was created by @Bahaaib on 29-Apr-19.

If you have any technical questions, don't ask me, submit new tickets instead. The task will be \"done\" when the problem is fixed and the text of the puzzle is _removed_ from the source code. Here is more about [PDD](http://www.yegor256.com/2009/03/04/pdd.html) and [about me](http://www.yegor256.com/2017/04/05/pdd-in-action.html).