All of our unit and integration tests are, currently, written to target MSTest. While this has worked fine for us historically, we have encountered some unexpected behavior lately, such as an inability to run parameterized tests. In addition, as xUnit.net has proven the dominant unit test library in the .NET ecosystem, most examples and extensions target it. Finally, using xUnit.net provides a lot improved tooling, including more Assert methods, as well as code analysis to ensure that they're being used correctly.

Much of the unit tests will be straight forward to migrate. Some of the unit tests, however, will be a bit more involved due to significant changes to the syntax—e.g., Assert.Throws<>(() => …) over [ExceptedException()].