Introduced unit test for validation of [FilterByAttribute()]

This validates that the validation within the `[FilterByAttribute()]` constructor (384f730) works as expected by raising an `ArgumentException` if the `Key` is set to `ContentType`. In that case, the implementation should instead use `[FilterByContentType()]`.

Author: JeremyCaney

OnTopic.Tests/TopicMappingServiceTest.cs

@@ -967,6 +967,25 @@ public async Task Map_FilterByAttribute_ReturnsFilteredCollection() {
 
     }
 
+    /*==========================================================================================================================
+    | TEST: MAP: FILTER BY INVALID ATTRIBUTE: THROWS EXCEPTION
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Attempts to map a view model that has an invalid <see cref="FilterByAttributeAttribute.Key"/> value of <c>ContentType
+    ///   </c>; throws an <see cref="ArgumentException"/>.
+    /// </summary>
+    [TestMethod]
+    [ExpectedException(typeof(ArgumentException))]
+    public async Task Map_FilterByInvalidAttribute_ThrowsExceptions() {
+
+      var topic                 = TopicFactory.Create("Test", "FilteredInvalid");
+
+      var target = await _mappingService.MapAsync<FilteredInvalidTopicViewModel>(topic).ConfigureAwait(false);
+
+      Assert.AreEqual<int>(2, target.Children.Count);
+
+    }
+
     /*==========================================================================================================================
     | TEST: MAP: FILTER BY CONTENT TYPE: RETURNS FILTERED COLLECTION
     \-------------------------------------------------------------------------------------------------------------------------*/

OnTopic.Tests/ViewModels/FilteredInvalidTopicViewModel.cs

@@ -0,0 +1,28 @@
+/*==============================================================================================================================
+| Author        Ignia, LLC
+| Client        Ignia, LLC
+| Project       Topics Library
+\=============================================================================================================================*/
+using OnTopic.Mapping.Annotations;
+using OnTopic.ViewModels;
+using OnTopic.ViewModels.Collections;
+
+namespace OnTopic.Tests.ViewModels {
+
+  /*============================================================================================================================
+  | VIEW MODEL: FILTERED TOPIC (INVALID)
+  \---------------------------------------------------------------------------------------------------------------------------*/
+  /// <summary>
+  ///   Provides a strongly-typed data transfer object for testing views properties annotated with the <see cref="
+  ///   FilterByAttributeAttribute"/>. Includes an invalid <see cref="FilterByAttributeAttribute"/>.
+  /// </summary>
+  /// <remarks>
+  ///   This is a sample class intended for test purposes only; it is not designed for use in a production environment.
+  /// </remarks>
+  public class FilteredInvalidTopicViewModel {
+
+    [FilterByAttribute("ContentType", "Page")]
+    public TopicViewModelCollection<TopicViewModel> Children { get; } = new();
+
+  } //Class
+} //Namespace