Implement passing test for ElementPickerViewModel.

Tests/ViewModels/ElementPickerViewModelTest.cs

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+/* ElementPickerViewModelTest.cs
+ * part of zaaReloaded2
+ * 
+ * Copyright 2015 Daniel Kraus
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+using Bovender.Mvvm.ViewModels;
+using zaaReloaded2.ViewModels;
+
+namespace Tests.ViewModels
+{
+    [TestFixture]
+    class ElementPickerViewModelTest
+    {
+        [Test]
+        public void ChooseElement()
+        {
+            ElementPickerViewModel vm = new ElementPickerViewModel(true);
+            ViewModelBase elementVM = vm.Categories.First().Children.First();
+            elementVM.IsSelected = true;
+            string expectedLabel = elementVM.DisplayString;
+
+            Assert.IsTrue(vm.ChooseElementCommand.CanExecute(null),
+                "Cannot execute ChooseElementCommand");
+
+            bool messageSent = false;
+            vm.ElementChosenMessage.Sent += (sender, args) =>
+            {
+                messageSent = true;
+                ViewModelBase messageContentVM = args.Content.ViewModel as ViewModelBase;
+                Assert.AreEqual(expectedLabel, messageContentVM.DisplayString);
+            };
+
+            vm.ChooseElementCommand.Execute(null);
+            Assert.IsTrue(messageSent, "No message was sent when element was chosen");
+        }
+    }
+}