Attribute [CollectionDefinition(DisableParallelization = true)] doesn't prevent parallel execution between class

[NinjaDev06]

I have a set of tests in some test classes that use a non-thread-safe resource. When I run all the tests in my solution, some of these tests fail because XUnit tests run in parallel when the tests are in a separate class.

I have tried this attribute on the class I want to disable parallelization and it does not matter.
[CollectionDefinition("EndpointTests", DisableParallelization = true)]

I'm using the XUnit and XUnit.runner.visualstudio at version 2.4.1.

I created a simple project that reproduce my problem when you run all tests in the solution.
XUnitTestProject.zip

[bradwilson]

You haven't properly defined the collection. The docs discuss how to do it: https://xunit.net/docs/shared-context#collection-fixture

My recommendation is that your tests look like this:

using System.Threading;
using Xunit;

namespace XUnitTestProject
{
    [Collection(nameof(NotThreadSafeResourceCollection))]
    public class UnitTest1
	{
		[Fact]
		public void Test1()
		{
			NotThreadSafeResource.Use();
			Thread.Sleep(1000);
			NotThreadSafeResource.Release();
		}

		[Fact]
		public void Test3()
		{
			NotThreadSafeResource.Use();
			Thread.Sleep(1000);
			NotThreadSafeResource.Release();
		}
	}
}

using System.Threading;
using Xunit;

namespace XUnitTestProject
{
    [Collection(nameof(NotThreadSafeResourceCollection))]
    public class UnitTest2
	{
		[Fact]
		public void Test2()
		{
			NotThreadSafeResource.Use();
			Thread.Sleep(1000);
			NotThreadSafeResource.Release();
		}
	}
}

And you should have an extra class, which is the collection definition class:

using Xunit;

namespace XUnitTestProject
{
    [CollectionDefinition(nameof(NotThreadSafeResourceCollection), DisableParallelization = true)]
    public class NotThreadSafeResourceCollection { }
}

[NinjaDev06]

Thanks you for your help! This fix my problem.

[mufasalg0]

Is it possible to run them in order? Without disabling the parallel execution for the whole framework?

I have found this:
https://github.com/tomaszeman/Xunit.Extensions.Ordering#test-cases-ordering

In order to run classes in order, I need to create AssemblyInfo.cs and add following lines in AssemblyInfo.cs

using Xunit;
//Optional
[assembly: CollectionBehavior(DisableTestParallelization = true)]
//Optional
[assembly: TestCaseOrderer("Xunit.Extensions.Ordering.TestCaseOrderer", "Xunit.Extensions.Ordering")]
//Optional
[assembly: TestCollectionOrderer("Xunit.Extensions.Ordering.CollectionOrderer", "Xunit.Extensions.Ordering")]

This causes to run whole framework with only one thread.

I would like to accomplish to put classes in order in selected Collection
For instance I have collection ("sequentialRun")

Collection[("sequentialRun"),Order(1)]
Class A{
 
[Fact]
 void test1(){}
[Fact]
 void test2(){}

}

Collection[("sequentialRun"),Order(2)]
Class B{

[Fact]
 void test1(){}
[Fact]
 void test2(){}
}

Class C{

[Fact]
 void test1(){}
[Fact]
 void test2(){}
}

When I trigger the whole test script in my framework I would like to achieve that A and C starts running together and when A is done then B can start. Is there anyway to accomplish this??

Thank you so much!!

[bradwilson]

I can't speak to specifically how that extension works, since I didn't write it and haven't ever used it.

What I can speak to is how parallelization works in general: https://xunit.net/docs/running-tests-in-parallel

This line is disabling parallelization:

[assembly: CollectionBehavior(DisableTestParallelization = true)]

Ordering should be orthogonal to parallelization.