At least I've wrote some FIT tests. FIT is an acceptance testing framework for business logic. So here are my first impressions:
- FIT tests are simpler to write than Unit tests. One of the main reason is external data. In FIT you set all data right in table, while in unit test you often set data in test method. Looks like useful separation.
- FIT is more convenient for integration tests. It is possible to create integration tests in XUnit, for example, but it takes more time
- Test tables could live with specification without any problems. You could include them in user story description, save document as html and use these html as input data for tests. Very simple and keep docs and tests in sync.
- But in general I don't see huge difference between FIT tests and Unit tests from developers point of view. The result is almost the same - the only difference is that test tables could be provided before development by customer. Well, on the other side, this difference is huge 🙂