Add Composer autoloading functions and PHPStan for testing

vendor/nikic/php-parser/test/PhpParser/ErrorHandler/ThrowingTest.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser\ErrorHandler;
+
+use PhpParser\Error;
+
+class ThrowingTest extends \PHPUnit\Framework\TestCase
+{
+    public function testHandleError() {
+        $this->expectException(Error::class);
+        $this->expectExceptionMessage('Test');
+        $errorHandler = new Throwing();
+        $errorHandler->handleError(new Error('Test'));
+    }
+}