Added unit tests to prevent regressions of issue #1100 that was fixed in v4

tests/UnitTests/SmartyMethodsTests/RegisterModifier/RegisterModifierFirstClassCallablesTest.php

@@ -0,0 +1,55 @@
+<?php
+// first class callables where introduced in PHP 8.1
+if (PHP_VERSION_ID >= 80100) {
+
+	/**
+	 * class for register modifier with (first class) callables tests
+	 *
+	 * @runTestsInSeparateProcess
+	 * @preserveGlobalState disabled
+	 * @backupStaticAttributes enabled
+	 */
+	class RegisterModifierFirstClassCallablesTest extends PHPUnit_Smarty
+	{
+		public function setUp(): void
+		{
+			$this->setUpSmarty(__DIR__);
+		}
+
+
+		public function testInit()
+		{
+			$this->cleanDirs();
+		}
+
+		public function testRegisterFirstClassCallable()
+		{
+			$this->smarty->registerPlugin(\Smarty\Smarty::PLUGIN_MODIFIER, 'testmodifier', eval('return strrev(...);'));
+			$this->assertEquals('mosredna', $this->smarty->fetch('string:{"andersom"|testmodifier}'));
+		}
+
+		public function testRegisterFirstClassCallableSameName()
+		{
+			$this->smarty->registerPlugin(\Smarty\Smarty::PLUGIN_MODIFIER, 'mymodifier', eval('return strrev(...);'));
+			$this->assertEquals('mosredna', $this->smarty->fetch('string:{"andersom"|mymodifier}'));
+		}
+
+		public function testRegisterFirstClassCallableAsFunc()
+		{
+			$this->smarty->registerPlugin(\Smarty\Smarty::PLUGIN_MODIFIER, 'kprint_r_out', eval('return strrev(...);'));
+			$this->smarty->assign('myVar', 'andersom');
+			$this->assertEquals('mosredna', $this->smarty->fetch('string:{kprint_r_out($myVar)}'));
+		}
+
+		public function testRegisterFirstClassCallableSameNameAsPhpFunc()
+		{
+			$this->smarty->registerPlugin(\Smarty\Smarty::PLUGIN_MODIFIER, 'mymodifierfcc', eval('return strrev(...);'));
+			$this->assertEquals('mosredna', $this->smarty->fetch('string:{mymodifierfcc("andersom")}'));
+		}
+
+	}
+}
+function mymodifierfcc($a, $b, $c)
+{
+	return "$a function $b $c";
+}