How do you filter xunit tests by trait with "dotnet test"? : <p>I have a .NET Core test project that uses Xunit 2.2. Some of my tests are marked with traits.</p>

<pre><code>[Fact]
[Trait("Color", "Blue")]
public void TestBlue()
{
}
</code></pre>

<p>What is the right command line syntax for "dotnet test" to only run tests where the trait Color == Blue ?</p>

<p>I'm using .NET Core CLI 1.0.0-rc4 which uses csproj, not project.json.</p>

<p>I'm trying to use <code>dotnet test --filter $something</code>, but whatever I use for $something, I see this error:</p>

<blockquote>
  <p>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.</p>
</blockquote>
