Optional Tests

There are different schools of thought on whether optional tests should be included. One way to look at it is that if it isn't absolutely necessary that a particular test pass, you shouldn't bother with it. This is fair; after all, your goal is to test the minimum necessary. Still, there's no rule that acceptance tests must pass 100% before the end of the iteration.

If you have time to perform noncritical tests and they pass, they'll give the customer extra confidence. If they fail, the customer can decide later whether to make the defects into stories to address them. Including noncritical tests isn't necessary, but it gives the customer more flexibility. Customers always have their mental lists of "must-haves" and "nice-to-haves"; if the "must-haves" don't take as much as estimated in the way of resources, the "nice-to-haves" are already defined and can be completed too.