Test run aborted when there are duplicate trait attributes

[jeremymeng]

Description

No helpful information to users when tests have duplicate trait attributes

Steps to reproduce

1. dotnet new -t xunittest
2. change the content of Tests.cs to the following

using System;
using System.Collections.Generic;
using System.Linq;
using Xunit;
using Xunit.Abstractions;
using Xunit.Sdk;

namespace Tests
{
    [Category(TestCategory.Async)]
    public class Tests
    {
        [Fact]
        [Category(TestCategory.Async)]
        public void Test1()
        {
            Assert.True(true);
        }
    }

    public enum TestCategory
    {
        Unspecified = 0,
        Async,
    }

    [TraitDiscoverer("Tests.CategoryDiscoverer", "xunittest")]
    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, AllowMultiple = true)]
    public class CategoryAttribute : Attribute, ITraitAttribute
    {
        public CategoryAttribute(TestCategory category)
        {
        }
    }

    public class CategoryDiscoverer : ITraitDiscoverer
    {
        public IEnumerable<KeyValuePair<string, string>> GetTraits(IAttributeInfo traitAttribute)
        {
            var args = traitAttribute.GetConstructorArguments().ToList();

            yield return new KeyValuePair<string, string>(args[0].ToString(), string.Empty);
        }
    }
}

3. dotnet restore
4. dotnet test

Expected behavior

Warning about duplicate attributes, but test should run

Actual behavior

Starting test execution, please wait...
Error: The active Test Run was aborted.

[codito]

@jeremymeng thanks for reporting this issue. It is fixed with #328. We will take the fix as part of next insertion to dotnet-cli.