Agile: tasks for testing or testing tasks?

I was wondering what does the standard recommend as best practice in this scenario:

When creating tasks for a user story we usually have development/design/documentation/testing tasks. Should we create a task for testing each testable development deliverable for should we test a development task before marking it as complete?

Do we create separate testing tasks (which of course can not be started before the corresponding dev task is complete and will cause a certain task dependency and priority to develop) or do we simply consider a task complete once it's tested? How do we mark it on the board in the latter scenario?