diff --git a/src/Framework/Environment.php b/src/Framework/Environment.php
index ab3e3748..2baba5e0 100644
--- a/src/Framework/Environment.php
+++ b/src/Framework/Environment.php
@@ -172,6 +172,27 @@ public static function getTestAnnotations()
 	}
 
 
+	/**
+	 * Removes keyword final from source codes.
+	 * @return void
+	 */
+	public static function bypassFinals()
+	{
+		FileMutator::addMutator(function ($code) {
+			if (strpos($code, 'final') !== false) {
+				$tokens = token_get_all($code);
+				$code = '';
+				foreach ($tokens as $token) {
+					$code .= is_array($token)
+						? ($token[0] === T_FINAL ? '' : $token[1])
+						: $token;
+				}
+			}
+			return $code;
+		});
+	}
+
+
 	/**
 	 * Loads data according to the file annotation or specified by Tester\Runner\TestHandler::initiateDataProvider()
 	 * @return array
diff --git a/src/Framework/FileMutator.php b/src/Framework/FileMutator.php
new file mode 100644
index 00000000..b4843b8a
--- /dev/null
+++ b/src/Framework/FileMutator.php
@@ -0,0 +1,212 @@
+<?php
+
+/**
+ * This file is part of the Nette Tester.
+ * Copyright (c) 2009 David Grudl (https://davidgrudl.com)
+ */
+
+namespace Tester;
+
+
+/**
+ * PHP file mutator.
+ */
+class FileMutator
+{
+	const PROTOCOL = 'file';
+
+	/** @var resource|null */
+	public $context;
+
+	/** @var resource|null */
+	private $handle;
+
+	/** @var callable[] */
+	private static $mutators = [];
+
+
+	public static function addMutator(callable $mutator)
+	{
+		self::$mutators[] = $mutator;
+		stream_wrapper_unregister(self::PROTOCOL);
+		stream_wrapper_register(self::PROTOCOL, __CLASS__);
+	}
+
+
+	public function dir_closedir()
+	{
+		closedir($this->handle);
+	}
+
+
+	public function dir_opendir($path, $options)
+	{
+		$this->handle = $this->native('opendir', $path, $this->context);
+		return (bool) $this->handle;
+	}
+
+
+	public function dir_readdir()
+	{
+		return readdir($this->handle);
+	}
+
+
+	public function dir_rewinddir()
+	{
+		return rewinddir($this->handle);
+	}
+
+
+	public function mkdir($path, $mode, $options)
+	{
+		return $this->native('mkdir', $mode, false, $this->context);
+	}
+
+
+	public function rename($pathFrom, $pathTo)
+	{
+		return $this->native('rename', $pathFrom, $pathTo, $this->context);
+	}
+
+
+	public function rmdir($path, $options)
+	{
+		return $this->native('rmdir', $this->context);
+	}
+
+
+	public function stream_cast($castAs)
+	{
+		return $this->handle;
+	}
+
+
+	public function stream_close()
+	{
+		fclose($this->handle);
+	}
+
+
+	public function stream_eof()
+	{
+		return feof($this->handle);
+	}
+
+
+	public function stream_flush()
+	{
+		return fflush($this->handle);
+	}
+
+
+	public function stream_lock($operation)
+	{
+		return flock($this->handle, $operation);
+	}
+
+
+	public function stream_metadata($path, $option, $value)
+	{
+		switch ($option) {
+			case STREAM_META_TOUCH:
+				return $this->native('touch', $path, $value[0], $value[1]);
+			case STREAM_META_OWNER_NAME:
+			case STREAM_META_OWNER:
+				return $this->native('chown', $path, $value);
+			case STREAM_META_GROUP_NAME:
+			case STREAM_META_GROUP:
+				return $this->native('chgrp', $path, $value);
+			case STREAM_META_ACCESS:
+				return $this->native('chmod', $path, $value);
+		}
+	}
+
+
+	public function stream_open($path, $mode, $options, &$openedPath)
+	{
+		$usePath = (bool) ($options & STREAM_USE_PATH);
+		if (pathinfo($path, PATHINFO_EXTENSION) === 'php') {
+			$content = $this->native('file_get_contents', $path, $usePath, $this->context);
+			if ($content === false) {
+				return false;
+			} else {
+				foreach (self::$mutators as $mutator) {
+					$content = call_user_func($mutator, $content);
+				}
+				$this->handle = tmpfile();
+				$this->native('fwrite', $this->handle, $content);
+				$this->native('fseek', $this->handle, 0);
+				return true;
+			}
+		} else {
+			$this->handle = $this->context
+				? $this->native('fopen', $path, $mode, $usePath, $this->context)
+				: $this->native('fopen', $path, $mode, $usePath);
+			return (bool) $this->handle;
+		}
+	}
+
+
+	public function stream_read($count)
+	{
+		return fread($this->handle, $count);
+	}
+
+
+	public function stream_seek($offset, $whence = SEEK_SET)
+	{
+		return fseek($this->handle, $offset, $whence);
+	}
+
+
+	public function stream_set_option($option, $arg1, $arg2)
+	{
+	}
+
+
+	public function stream_stat()
+	{
+		return fstat($this->handle);
+	}
+
+
+	public function stream_tell()
+	{
+		return ftell($this->handle);
+	}
+
+
+	public function stream_truncate($newSize)
+	{
+		return ftruncate($this->handle, $newSize);
+	}
+
+
+	public function stream_write($data)
+	{
+		return fwrite($this->handle, $data);
+	}
+
+
+	public function unlink($path)
+	{
+		return $this->native('unlink', $path);
+	}
+
+
+	public function url_stat($path, $flags)
+	{
+		return $this->native('fstat', $path, $flags);
+	}
+
+
+	private function native($func)
+	{
+		stream_wrapper_restore(self::PROTOCOL);
+		$res = call_user_func_array($func, array_slice(func_get_args(), 1));
+		stream_wrapper_unregister(self::PROTOCOL);
+		stream_wrapper_register(self::PROTOCOL, __CLASS__);
+		return $res;
+	}
+}
diff --git a/src/bootstrap.php b/src/bootstrap.php
index 51366b9c..f2f18b2c 100644
--- a/src/bootstrap.php
+++ b/src/bootstrap.php
@@ -13,6 +13,7 @@
 require __DIR__ . '/Framework/FileMock.php';
 require __DIR__ . '/Framework/TestCase.php';
 require __DIR__ . '/Framework/DomQuery.php';
+require __DIR__ . '/Framework/FileMutator.php';
 require __DIR__ . '/CodeCoverage/Collector.php';
 require __DIR__ . '/Runner/Job.php';
 
diff --git a/tests/Framework/FileMutator.phpt b/tests/Framework/FileMutator.phpt
new file mode 100644
index 00000000..8e1ca74d
--- /dev/null
+++ b/tests/Framework/FileMutator.phpt
@@ -0,0 +1,14 @@
+<?php
+
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+Tester\Environment::bypassFinals();
+
+require __DIR__ . '/fixtures/final.class.php';
+
+$rc = new ReflectionClass('FinalClass');
+Assert::false($rc->isFinal());
+Assert::false($rc->getMethod('finalMethod')->isFinal());
diff --git a/tests/Framework/fixtures/final.class.php b/tests/Framework/fixtures/final.class.php
new file mode 100644
index 00000000..410c0ab3
--- /dev/null
+++ b/tests/Framework/fixtures/final.class.php
@@ -0,0 +1,8 @@
+<?php
+
+final class FinalClass
+{
+	final function finalMethod()
+	{
+	}
+}
diff --git a/tests/coding-standard.neon b/tests/coding-standard.neon
index b2bed969..c76d1ab4 100644
--- a/tests/coding-standard.neon
+++ b/tests/coding-standard.neon
@@ -5,3 +5,4 @@ parameters:
 	skip:
 		PHP_CodeSniffer\Standards\PSR1\Sniffs\Methods\CamelCapsMethodNameSniff:
 			- src/Framework/FileMock.php
+			- src/Framework/FileMutator.php