We solved this problem as follows:
- Every item in the product backlog must have fit criteria or acceptance criteria,
without those, we don't start a sprint
- A tester is part of our team, for every product backlog item, he creates test tasks (1 or more, based on the acceptance criteria) together with an estimation, and a link to the item to test
- During the daily scrum, all tasks that are finished are placed in a 'To Test' column
- We never do tasks that take longer than 16 hours; tasks that are estimated longer, are split up
