Q:

How to perform global setup/teardown in xUnit and run tests in parallel?

Here is what I want to achieve with xUnit: 

Run initialization code.
Run tests in parallel.
Perform teardown.

I have tried [CollectionDefinition]/[Collection]/ICollectionFixture
approach described here but it has disabled the parallel execution, which is critical for me.
Are there any way to run tests in parallel and be able to write global setup/tear-down code in xUnit?
If it is not possible with xUnit, does NUnit or MSUnit support this scenario?

A:

NUnit supports this scenario. For global setup, create a class in one of your root namespaces and add the [SetupFixture] attribute to it. Then add a [OneTimeSetUp] method to that class. This method will get run once for all tests in that namespace and in child namespaces. This allows you to have additional namespace specific onetime setups.
[SetUpFixture]
public class MySetUpClass
{
  [OneTimeSetUp]
  public void RunBeforeAnyTests()
  {
    // ...
  }

  [OneTimeTearDown]
  public void RunAfterAnyTests()
  {
    // ...
  }
}

Then to run your tests in parallel, add the [Parallelizable] attribute at the assembly level with the ParallelScope.All. If you have tests that should not be run in parallel with others, you can use the NonParallelizable attribute at lower levels.
[assembly: Parallelizable(ParallelScope.All)]
Running test methods in parallel in NUnit is supported in NUnit 3.7 and later. Prior to that, it only supported running test classes in parallel. I would recommend starting any project with the most recent version of NUnit to take advantages of bug fixes, new features and improvements.

