Ideally you'd get both engineers writing tests for their code as well QA teams for products.
Indeed, but there is also a good reason that professional editors have new writing proofread or even technically reviewed by people other than the original author.
Maybe there's some subtlety that I'm not picking up here about Microsoft's previous set-up and/or the model they've been moving to under Nadella's leadership. We seem to have some past and present Microsoft developers around these parts, so perhaps their comments will clarify this. But as reported, this looks to me like a retrograde step, an attempt to be more agile and fast-moving rather than something likely to improve the quality of the finished product.