In order for developers to be able develop exactly what is required, validation or acceptance tests must be added to user stories. Each User Story should be able to have numerous Acceptance/Validation tests. This will assist in assigning effort and ensuring the the quality of the development is high.
|Release time frame|
This can be achieved through the use of Requirements.
In the Requirements sections for your User Stories (Features), you can create separate requirements for each validation test. This can help the team in estimating effort and ensuring high quality development. You may also consider pre-pending the requirement with text around "Validation test" so that you can differentiate them.