Parallel settings do not work when using AssemblyFixture

[ppasieka]

In the xunit.runner.json file you can specify rules related to parallel execution.

{
  "$schema": "https://xunit.net/schema/current/xunit.runner.schema.json",
  "maxParallelThreads": 4,
  "parallelizeTestCollections": true,
  "parallelizeAssembly": true
}

I compared commits with and without the IAssemblyFixture applied to my tests.
With the above configuration and when using classic IClassFixture, the maximal number of running tests is 4.

But with the AssembluFixture, the test runner executes tests without limits (approx ~120 tests at the same time)

Is there a way to control it?

[Kurzyn]

I've looked at code there and it seems like:

in base.AfterTestAssemblyStartingAsync is calling Initialize()

and there runner is looking for CollectionBehaviorAttribute and with that you could add DisableTestParallelization and MaxParallelThreads

protected void Initialize()
        {
            if (initialized)
                return;

            collectionBehaviorAttribute = TestAssembly.Assembly.GetCustomAttributes(typeof(CollectionBehaviorAttribute)).SingleOrDefault();
            if (collectionBehaviorAttribute != null)
            {
                disableParallelization = collectionBehaviorAttribute.GetNamedArgument<bool>("DisableTestParallelization");
                maxParallelThreads = collectionBehaviorAttribute.GetNamedArgument<int>("MaxParallelThreads");
            }

            disableParallelization = ExecutionOptions.DisableParallelization() ?? disableParallelization;
            maxParallelThreads = ExecutionOptions.MaxParallelThreads() ?? maxParallelThreads;
            if (maxParallelThreads == 0)
                maxParallelThreads = Environment.ProcessorCount;

            var testCaseOrdererAttribute = TestAssembly.Assembly.GetCustomAttributes(typeof(TestCaseOrdererAttribute)).SingleOrDefault();
            if (testCaseOrdererAttribute != null)
            {
                try
                {
                    var testCaseOrderer = ExtensibilityPointFactory.GetTestCaseOrderer(DiagnosticMessageSink, testCaseOrdererAttribute);
                    if (testCaseOrderer != null)
                        TestCaseOrderer = testCaseOrderer;
                    else
                    {
                        var args = testCaseOrdererAttribute.GetConstructorArguments().Cast<string>().ToList();
                        DiagnosticMessageSink.OnMessage(new DiagnosticMessage($"Could not find type '{args[0]}' in {args[1]} for assembly-level test case orderer"));
                    }
                }
                catch (Exception ex)
                {
                    var innerEx = ex.Unwrap();
                    var args = testCaseOrdererAttribute.GetConstructorArguments().Cast<string>().ToList();
                    DiagnosticMessageSink.OnMessage(new DiagnosticMessage($"Assembly-level test case orderer '{args[0]}' threw '{innerEx.GetType().FullName}' during construction: {innerEx.Message}{Environment.NewLine}{innerEx.StackTrace}"));
                }
            }

            var testCollectionOrdererAttribute = TestAssembly.Assembly.GetCustomAttributes(typeof(TestCollectionOrdererAttribute)).SingleOrDefault();
            if (testCollectionOrdererAttribute != null)
            {
                try
                {
                    var testCollectionOrderer = ExtensibilityPointFactory.GetTestCollectionOrderer(DiagnosticMessageSink, testCollectionOrdererAttribute);
                    if (testCollectionOrderer != null)
                        TestCollectionOrderer = testCollectionOrderer;
                    else
                    {
                        var args = testCollectionOrdererAttribute.GetConstructorArguments().Cast<string>().ToList();
                        DiagnosticMessageSink.OnMessage(new DiagnosticMessage($"Could not find type '{args[0]}' in {args[1]} for assembly-level test collection orderer"));
                    }
                }
                catch (Exception ex)
                {
                    var innerEx = ex.Unwrap();
                    var args = testCollectionOrdererAttribute.GetConstructorArguments().Cast<string>().ToList();
                    DiagnosticMessageSink.OnMessage(new DiagnosticMessage($"Assembly-level test collection orderer '{args[0]}' threw '{innerEx.GetType().FullName}' during construction: {innerEx.Message}{Environment.NewLine}{innerEx.StackTrace}"));
                }
            }

            initialized = true;
        }