Fix task collection attach relation

tests/Unit/TaskCollectionsRelationTest.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Tests\Unit;
+
+use App\Models\Task;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
+use Tests\TestCase;
+
+class TaskCollectionsRelationTest extends TestCase
+{
+    public function test_task_has_task_collections_relation(): void
+    {
+        $task = new Task;
+        $relation = $task->taskCollections();
+
+        $this->assertInstanceOf(BelongsToMany::class, $relation);
+        $this->assertSame(['sort_order'], $relation->getPivotColumns());
+    }
+}