TestPriority.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xunit;
using Xunit.Sdk;
using Xunit.Abstractions;

namespace XmlSchemaClassGenerator.Tests
{
    public class PriorityOrderer : ITestCaseOrderer
    {
        public IEnumerable<TTestCase> OrderTestCases<TTestCase>(IEnumerable<TTestCase> testCases) where TTestCase : ITestCase
        {
            var sortedMethods = new SortedDictionary<int, List<TTestCase>>();

            foreach (TTestCase testCase in testCases)
            {
                int priority = 0;

                foreach (IAttributeInfo attr in testCase.TestMethod.Method.GetCustomAttributes((typeof(TestPriorityAttribute).AssemblyQualifiedName)))
                    priority = attr.GetNamedArgument<int>("Priority");

                GetOrCreate(sortedMethods, priority).Add(testCase);
            }

            foreach (var list in sortedMethods.Keys.Select(priority => sortedMethods[priority]))
            {
                list.Sort((x, y) => StringComparer.OrdinalIgnoreCase.Compare(x.TestMethod.Method.Name, y.TestMethod.Method.Name));
                foreach (TTestCase testCase in list)
                    yield return testCase;
            }
        }

        static TValue GetOrCreate<TKey, TValue>(IDictionary<TKey, TValue> dictionary, TKey key) where TValue : new()
        {
            if (dictionary.TryGetValue(key, out TValue result)) return result;

            result = new TValue();
            dictionary[key] = result;

            return result;
        }
    }

    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
    public sealed class TestPriorityAttribute : Attribute
    {
        public TestPriorityAttribute(int priority)
        {
            Priority = priority;
        }

        public int Priority { get; private set; }
    }
}