Add TaskAssignEventSubscriber unit tests

- Covered `getSubscribedEvents` method behavior
- Added tests for `onTaskAssigned` with changed and unchanged assignees
- Validated notification properties in appropriate scenarios

src/Bundle/ChillTaskBundle/Tests/EventSubscriber/TaskAssignEventSubscriberTest.php

@@ -0,0 +1,119 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Chill\TaskBundle\Tests\EventSubscriber;
+
+use Chill\MainBundle\Entity\Notification;
+use Chill\MainBundle\Entity\User;
+use Chill\TaskBundle\Entity\SingleTask;
+use Chill\TaskBundle\Event\AssignTaskEvent;
+use Chill\TaskBundle\Event\TaskAssignEventSubscriber;
+use Chill\TaskBundle\Notification\AssignTaskNotificationFlagProvider;
+use Doctrine\ORM\EntityManagerInterface;
+use PHPUnit\Framework\TestCase;
+use Twig\Environment;
+
+class TaskAssignEventSubscriberTest extends TestCase
+{
+    private EntityManagerInterface $entityManager;
+    private Environment $twig;
+    private TaskAssignEventSubscriber $subscriber;
+
+    protected function setUp(): void
+    {
+        $this->entityManager = $this->createMock(EntityManagerInterface::class);
+        $this->twig = $this->createMock(Environment::class);
+        $this->subscriber = new TaskAssignEventSubscriber($this->entityManager, $this->twig);
+    }
+
+    public function testGetSubscribedEvents(): void
+    {
+        $events = TaskAssignEventSubscriber::getSubscribedEvents();
+
+        $this->assertArrayHasKey(AssignTaskEvent::PERSIST, $events);
+        $this->assertEquals(['onTaskAssigned', 0], $events[AssignTaskEvent::PERSIST]);
+    }
+
+    public function testOnTaskAssignedCreatesNotificationWhenAssigneeChanges(): void
+    {
+        // Arrange
+        $task = $this->createMock(SingleTask::class);
+        $assignee = $this->createMock(User::class);
+        $event = $this->createMock(AssignTaskEvent::class);
+
+        $task->method('getId')->willReturn(123);
+        $task->method('getTitle')->willReturn('Test Task');
+        $task->method('getAssignee')->willReturn($assignee);
+
+        $event->method('hasAssigneeChanged')->willReturn(true);
+        $event->method('getTask')->willReturn($task);
+
+        $this->twig->expects($this->exactly(2))
+            ->method('render')
+            ->with(
+                $this->logicalOr(
+                    '@ChillTask/Notification/task_assignment_notification_title.txt.twig',
+                    '@ChillTask/Notification/task_assignment_notification_content.txt.twig'
+                ),
+                $this->isType('array')
+            )
+            ->willReturnOnConsecutiveCalls('Notification Title', 'Notification Content');
+
+        $this->entityManager->expects($this->once())
+            ->method('persist')
+            ->with($this->isInstanceOf(Notification::class));
+
+        // Act
+        $this->subscriber->onTaskAssigned($event);
+    }
+
+    public function testOnTaskAssignedDoesNothingWhenAssigneeDoesNotChange(): void
+    {
+        // Arrange
+        $event = $this->createMock(AssignTaskEvent::class);
+        $event->method('hasAssigneeChanged')->willReturn(false);
+
+        $this->twig->expects($this->never())->method('render');
+        $this->entityManager->expects($this->never())->method('persist');
+
+        // Act
+        $this->subscriber->onTaskAssigned($event);
+    }
+
+    public function testNotificationHasCorrectProperties(): void
+    {
+        // Arrange
+        $task = $this->createMock(SingleTask::class);
+        $assignee = $this->createMock(User::class);
+        $event = $this->createMock(AssignTaskEvent::class);
+
+        $task->method('getId')->willReturn(456);
+        $task->method('getTitle')->willReturn('Important Task');
+        $task->method('getAssignee')->willReturn($assignee);
+
+        $event->method('hasAssigneeChanged')->willReturn(true);
+        $event->method('getTask')->willReturn($task);
+
+        $this->twig->method('render')->willReturn('Test Content');
+
+        // Capture the persisted notification
+        $persistedNotification = null;
+        $this->entityManager->expects($this->once())
+            ->method('persist')
+            ->willReturnCallback(function ($notification) use (&$persistedNotification) {
+                $persistedNotification = $notification;
+            });
+
+        // Act
+        $this->subscriber->onTaskAssigned($event);
+
+        // Assert
+        $this->assertInstanceOf(Notification::class, $persistedNotification);
+        $this->assertEquals(456, $persistedNotification->getRelatedEntityId());
+        $this->assertEquals(SingleTask::class, $persistedNotification->getRelatedEntityClass());
+        $this->assertEquals(AssignTaskNotificationFlagProvider::FLAG, $persistedNotification->getType());
+        $this->assertEquals('Test Content', $persistedNotification->getTitle());
+        $this->assertEquals('Test Content', $persistedNotification->getMessage());
+    }
+}