Added test case for serializing with PlaylistElementConverter

SpotifyAPI.Web.Tests/Models/PlayableItemConverterTest.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using Newtonsoft.Json;
+using NUnit.Framework;
+
+namespace SpotifyAPI.Web.Tests
+{
+  [TestFixture]
+  public class PPlayableItemConverterTest
+  {
+    [Test]
+    public void PlayableItemConverter_CanSerialize()
+    {
+      var context = new CurrentlyPlayingContext { Item = new FullTrack() };
+
+      Assert.DoesNotThrow(() =>
+      {
+        var serialized = JsonConvert.SerializeObject(context);
+      });
+    }
+  }
+}