To ensure that delivered product meets the END user’s requirements it is important that sufficient testing is done and all scenarios are tested.
Sufficient Test Coverage in an Agile Development Scenario may be TRICKY but with close cooperation and the right TEAM dynamics it may not be IMPOSSIBLE.
The objectives of the Project should be clear to the entire team. Many teams advocate Test Driven Development. At every stage the Software is tested if it meets the Requirements. Every Requirement is translated to a Test Case and Software is validated/ verified. While the Processes and Documentation are not stressed upon sufficient steps are taken to ensure that the software is delivered as per the User EXPECTATIONS. This implies that each Software delivery should be tested thoroughly before it is released.
The timelines being short requires that the person testing the software has sufficient knowledge about the system and its objectives.