AsyncNamingConventionTests.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using Xunit;

namespace MyProject.Tests
{
    public class AsyncNamingConventionTests
    {
        [Fact]
        public void AsyncMethodNamesShouldBePostfixedWithAsync()
        {
            var webAssembly = typeof(Program).Assembly;

            var incorrectlyNamedMethods = webAssembly
                .GetTypes()
                .SelectMany(x => x.GetMethods())
                .Where(x => x.ReturnType == typeof(Task) || x.ReturnType.IsGenericTask())
                .Where(x => !x.Name.EndsWith("Async"));

            if(incorrectlyNamedMethods.Any())
            {
                foreach(var method in incorrectlyNamedMethods)
                {
                    Console.WriteLine($"{method.DeclaringType.Name}.cs(0,0): {method.Name}");
                }

                Assert.True(false, "Async method names do not end with Async. See test output for details.");
            }
        }
    }

    public static class TypeExtension
    {
        public static bool IsGenericTask(this Type type)
        {
            return 
                type.IsGenericType &&
                type.GetGenericTypeDefinition() == typeof(Task<>);
        }
    }
}