test(ui/templates): cover drag-template-to-root via bUnit DragEventArgs

src/ScadaLink.CentralUI/Components/Pages/Design/Templates.razor

@@ -144,7 +144,8 @@
                 </div>
 
                 <div style="max-height: calc(100vh - 160px); overflow-y: auto;">
-                    <div @ondragover:preventDefault="true" @ondrop="OnDropOnRoot"
+                    <div class="templates-root-dropzone"
+                         @ondragover:preventDefault="true" @ondrop="OnDropOnRoot"
                          style="min-height: 100%; padding: 4px;">
                         <TreeView @ref="_tree" TItem="TmplNode" Items="_treeRoots"
                                   ChildrenSelector="n => n.Children"

tests/ScadaLink.CentralUI.Tests/TemplatesPageTests.cs

@@ -1,6 +1,7 @@
 using System.Security.Claims;
 using Bunit;
 using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.AspNetCore.Components.Web;
 using Microsoft.Extensions.DependencyInjection;
 using NSubstitute;
 using ScadaLink.Commons.Entities.Templates;
@@ -118,6 +119,42 @@ public class TemplatesPageTests : BunitContext
         Assert.Contains("DelmiaReceiver", cut.Markup);
         Assert.Contains("→", cut.Markup);
     }
+
+    [Fact]
+    public async Task DragTemplateOntoRoot_CallsMoveTemplateAsync_WithNullFolderId()
+    {
+        // Arrange: one template currently parented to a folder; the test simulates
+        // the user dragging that template onto the root drop-zone, which should
+        // result in TemplateService.MoveTemplateAsync(..., newFolderId: null) being
+        // invoked. We keep the template at the root in the rendered tree (FolderId
+        // null) so it renders without needing an expand-click; the drag payload only
+        // cares about the in-memory id captured by OnDragStart, not the visual
+        // parent.
+        var template = new Template("RootDragTarget") { Id = 5, FolderId = null };
+        _repo.GetAllTemplatesAsync(Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<Template>>(new List<Template> { template }));
+        _repo.GetAllFoldersAsync(Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<TemplateFolder>>(new List<TemplateFolder>()));
+        _repo.GetTemplateByIdAsync(5, Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<Template?>(template));
+
+        var cut = Render<TemplatesPage>();
+
+        // Act: fire ondragstart on the template's draggable <div> (RenderNodeLabel
+        // emits draggable="true" for template/folder nodes), then ondrop on the
+        // root wrapper marked with the test-affordance class added to the page.
+        var templateNode = cut.Find("div[draggable='true']");
+        await templateNode.TriggerEventAsync("ondragstart", new DragEventArgs());
+
+        var rootDropZone = cut.Find("div.templates-root-dropzone");
+        await rootDropZone.TriggerEventAsync("ondrop", new DragEventArgs());
+
+        // Assert: TemplateService.MoveTemplateAsync delegates to the repository's
+        // UpdateTemplateAsync with FolderId set to null.
+        await _repo.Received(1).UpdateTemplateAsync(
+            Arg.Is<Template>(t => t.Id == 5 && t.FolderId == null),
+            Arg.Any<CancellationToken>());
+    }
 }
 
 internal sealed class TestAuthStateProvider : AuthenticationStateProvider