Fixed broken unit tests caused by using RunSettings in new code

src/NUnitTestAdapterTests/Fakes/FakeRunContext.cs

@@ -71,7 +71,7 @@ namespace NUnit.VisualStudio.TestAdapter.Tests.Fakes
 
         IRunSettings IDiscoveryContext.RunSettings
         {
-            get { throw new NotImplementedException(); }
+            get { return new FakeRunSettings(); }
         }
 
         #endregion

src/NUnitTestAdapterTests/Fakes/FakeRunSettings.cs

@@ -35,7 +35,7 @@ namespace NUnit.VisualStudio.TestAdapter.Tests.Fakes
 
         public string SettingsXml
         {
-            get { throw new NotImplementedException(); }
+            get { return string.Empty; }
         }
     }
 }