Added missing todo marker test

Author: rubberduck203

RubberduckTests/ConfigurationTests.cs

@@ -1,4 +1,5 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System.Runtime.InteropServices;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Rubberduck.Settings;
 
 namespace RubberduckTests
@@ -37,5 +38,14 @@ public void DefaultCodeInspectionsIsNotNull()
 
             Assert.IsNotNull(config);
         }
+
+        [TestMethod]
+        public void ToStringIsAsExpected()
+        {
+            var expected = "FixMe:";
+            var marker = new ToDoMarker(expected, TodoPriority.High);
+
+            Assert.AreEqual(expected, marker.ToString());
+        }
     }
 }