I'm writing unit tests using Selenium and xunit and on their own they run great but if I select all of the tests (multiple classes) in Test Explorer (they appear to be grouped by class - this is not intentional) they run in parallel. Run Tests in Parallel is not selected. Each one of my tests creates and then deletes test data so they obviously can't run in parallel. One test might delete data right after another test created that data and so the test would fail. So how can I run all of my tests and not have them run in parallel? I guess I could make them all use one partial class that spans multiple files but that's not my first choice.
I found a solution (although not an explanation). Just put [Collection("Sequential")] as the first line under each namespace. This forces everything to run sequentially.