Added CancelTaskException (#4186)

tests/phpunit/scheduler/TaskSchedulerTest.php

@@ -0,0 +1,48 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\scheduler;
+
+use PHPUnit\Framework\TestCase;
+
+class TaskSchedulerTest extends TestCase{
+
+	/** @var TaskScheduler */
+	private $scheduler;
+
+	public function setUp() : void{
+		$this->scheduler = new TaskScheduler();
+	}
+
+	public function tearDown() : void{
+		$this->scheduler->shutdown();
+	}
+
+	public function testCancel() : void{
+		$task = $this->scheduler->scheduleTask(new ClosureTask(function() : void{
+			throw new CancelTaskException();
+		}));
+		$this->scheduler->mainThreadHeartbeat(0);
+		self::assertTrue($task->isCancelled(), "Task was not cancelled");
+	}
+}