I’m mixed on unit tests - there are some things the developer will know (white box) about edge cases etc. that others likely wouldn’t, and they should definitely have input on those tests. On the other hand, independence of review is a very important aspect of “harnessing the power of the team.” If you’ve got one guy who gathers the requirements, implements the code, writes the tests, and declares the requirements fulfilled, that better be one outstandingly brilliant guy with all the time on his hands he needs to do the jobs right. If you’re trying to leverage the talents of 20 people to make a better product, having them all be solo-virtuoso actors working independently alongside each other is more likely to create conflict, chaos, duplication, and massive holes of missed opportunities and unforeseen problems in the project.