Q:

How do you filter xunit tests by trait with "dotnet test"?

I have a .NET Core test project that uses Xunit 2.2. Some of my tests are marked with traits.
[Fact]
[Trait("Color", "Blue")]
public void TestBlue()
{
}

What is the right command line syntax for "dotnet test" to only run tests where the trait Color == Blue ?
I'm using .NET Core CLI 1.0.0-rc4 which uses csproj, not project.json.
I'm trying to use dotnet test --filter $something, but whatever I use for $something, I see this error:

Error: [xUnit.net 00:00:00.7800155] E2ETests: Exception filtering tests: No tests matched the filter because it contains one or more properties that are not valid ($something). Specify filter expression containing valid properties (DisplayName, FullyQualifiedName) and try again.

A:

I found the answer  (only tests attributed [Trait("TraitName", "TraitValue")] are executed):
dotnet test --filter TraitName=TraitValue

Alternatively, you can filter by not having a trait value (tests attributed [Trait("TraitName", "TraitValue")] are execluded from run) 
dotnet test --filter TraitName!=TraitValue

In my example above, this means I can run:
dotnet test --filter Color=Blue

More docs here: https://github.com/Microsoft/vstest-docs/blob/master/docs/filter.md

A:

In the csproj
<PropertyGroup>
  <TargetFramework>netcoreapp2.0</TargetFramework>
</PropertyGroup>
<ItemGroup>
  <PackageReference Include="xunit" Version="2.3.0" />
  <DotNetCliToolReference Include="dotnet-xunit" Version="2.3.0" />
</ItemGroup>

command line
dotnet xunit -trait "Color=Blue"

