New test

ActiveDirectoryQuerier.Tests/ActiveDirectoryQuerier.Tests.csproj

@@ -8,6 +8,7 @@
 
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
+        <PackageReference Include="Moq" Version="4.20.70" />
         <PackageReference Include="xunit" Version="2.7.0" />
         <PackageReference Include="xunit.runner.visualstudio" Version="2.5.7">
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

ActiveDirectoryQuerier.Tests/MainWindowViewModelTests.cs

@@ -0,0 +1,27 @@
+using System.Windows;
+using ActiveDirectoryQuerier.MessageBoxService;
+using Moq;
+
+namespace ActiveDirectoryQuerier.Tests;
+
+public class MainWindowViewModelTests
+{
+    [Fact]
+    public void EditQueryFromQueryStackPanel_NullParameter_ShowsMessageBox()
+    {
+        // Arrange
+        var mockMessageBoxService = new Mock<IMessageBoxService>();
+        var viewModel = new MainWindowViewModel
+        {
+            MessageBoxService = mockMessageBoxService.Object
+        };
+
+        // Act
+        viewModel.EditQueryFromQueryStackPanel(null);
+
+        // Assert
+        mockMessageBoxService.Verify(
+            x => x.Show(It.IsAny<string>(), "Error", MessageBoxButton.OK, MessageBoxImage.Error),
+            Times.Once);
+    }
+}