Add Specification trait (#23)

* create specification trait

* rename to specification

src/Xunit.Categories/SpecificationAttribute.cs

@@ -0,0 +1,28 @@
+using System;
+using Xunit.Sdk;
+
+namespace Xunit.Categories
+{
+    [TraitDiscoverer(SpecificationDiscoverer.DiscovererTypeName, DiscovererUtil.AssemblyName)]
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true)]
+    public class SpecificationAttribute:Attribute, ITraitAttribute
+    {
+        public SpecificationAttribute()
+        {
+
+        }
+
+        public SpecificationAttribute(string id)
+        {
+            this.Identifier = id;
+        }
+
+        public SpecificationAttribute(long id)
+        {
+            this.Identifier = id.ToString();
+        }
+
+        public string Identifier { get; private set; }
+
+    }
+}

src/Xunit.Categories/SpecificationDiscoverer.cs

@@ -0,0 +1,21 @@
+using System.Collections.Generic;
+using Xunit.Abstractions;
+using Xunit.Sdk;
+
+namespace Xunit.Categories
+{
+    public class SpecificationDiscoverer:ITraitDiscoverer
+    {
+        internal const string DiscovererTypeName = DiscovererUtil.AssemblyName + "." + nameof(SpecificationDiscoverer);
+
+        public IEnumerable<KeyValuePair<string, string>> GetTraits(IAttributeInfo traitAttribute)
+        {
+            var name = traitAttribute.GetNamedArgument<string>("Identifier");
+
+            yield return new KeyValuePair<string, string>("Category", "Specification");
+
+            if (!string.IsNullOrWhiteSpace(name))
+                yield return new KeyValuePair<string, string>("Specification", name);
+        }
+    }
+}

test/Xunit.Categories.Test/Scratch.cs

@@ -66,6 +66,16 @@ public void TestExploratory()
             throw new NotImplementedException("I'm not that important, all the world knows about me, I'll be fixed in 2030");
         }
 
+
+        [Fact]
+        [Specification]
+        [Specification(666)]
+        [Specification("666 a")]
+        public void TestSpecification()
+        {
+            throw new NotImplementedException("I'm not that important, all the world knows about me, I'll be fixed in 2030");
+        }
+
         [Fact]
         [WorkItem]
         [WorkItem(666)]