fix: TasksPopulation_IsIdempotent

Author: Xiphereal

Desktop.Tests/TestAPI/InMemoryTaskRepository.cs

@@ -0,0 +1,36 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Desktop.Tasks;
+
+namespace Desktop.Tests.TestAPI;
+
+using SystemTask = Task;
+
+public class InMemoryTaskRepository : ITaskRepository
+{
+    private readonly List<Domain.Task> tasks = [];
+
+    public InMemoryTaskRepository(IEnumerable<Domain.Task> with)
+    {
+        tasks.AddRange(with);
+    }
+
+    public Task<IReadOnlyList<Domain.Task>> All()
+    {
+        return SystemTask.FromResult<IReadOnlyList<Domain.Task>>(tasks.ToArray());
+    }
+
+    public SystemTask Save(Domain.Task task)
+    {
+        tasks.Add(task);
+
+        return SystemTask.CompletedTask;
+    }
+
+    public SystemTask Delete(Domain.Task toBeDeleted)
+    {
+        tasks.Remove(toBeDeleted);
+
+        return SystemTask.CompletedTask;
+    }
+}

Desktop.Tests/TestAPI/Utils.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace Desktop.Tests.TestAPI;
+
+public class Utils
+{
+    public const int SeveralTimes = 5;
+
+    public static void Repeat(Action what, int times)
+    {
+        for (var i = 0; i < times; i++)
+            what();
+    }
+}

Desktop.Tests/UnitTests/TaskListViewModelTests.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Threading.Tasks;
+using Desktop.Project;
+using Desktop.Tasks;
+using Desktop.Tests.TestAPI;
+using FluentAssertions;
+using NUnit.Framework;
+using static Desktop.Tests.TestAPI.TaskFactory;
+using static Desktop.Tests.TestAPI.Utils;
+
+namespace Desktop.Tests.UnitTests;
+
+public class TaskListViewModelTests
+{
+    [Test]
+    [Category("Regression")]
+    public async Task TasksPopulation_IsIdempotent()
+    {
+        var taskRepository = new InMemoryTaskRepository([DesktopTask()]);
+        var sut = TaskListViewModel(taskRepository);
+
+        Repeat(sut.PopulateTasks, SeveralTimes);
+
+        sut.Tasks.Should().BeEquivalentTo(await taskRepository.All());
+    }
+
+    private static TaskListViewModel TaskListViewModel(InMemoryTaskRepository taskRepository)
+    {
+        return new TaskListViewModel(
+            taskRepository,
+            new TaskCreationViewModel(taskRepository));
+    }
+}

Desktop/Project/TaskListViewModel.cs

@@ -44,6 +44,8 @@ public TaskListViewModel(
 
     public void PopulateTasks()
     {
+        Tasks.Clear();
+
         // TODO: load this async and deferred from the ctor.
         var retrievedTasks = SystemTask.Run(taskRepository.All).Result;
         foreach (var task in retrievedTasks)

Desktop/TODO.md

@@ -1,5 +1,4 @@
-- fix: Tasks are duplicated when reloading Task List view
-- docs: project directory structure: vertical slicing vs by tech.
+- docs: project directory structure: vertical slicing vs by tech.
 - docs: the focus on UX with the accelerators/shortcuts.
 - docs: when and why use comments & summaries.
 - refactor: use Commands and ViewModels instead of code behinds.