Items are 'Done' when they are complete based on the definition of 'Done'. In that case, they would have the potential of creating a releasable/shippable Increment that is usable by the end user. Tests are also part of the work and items
are not 'Done' before the tests are complete; even the user acceptance tests. Quality requirements are part of the work but not all of it (eg non-functional features and development processes are also part of the work). We cannot trust
the identified tasks because we might have missed some tasks and the sum of them do not conform to the definition of 'Done'.