public static function overwriteFunction($name, $callback = null) {
		if ($name === false) {
			static::$_functionResults = [];
			return static::$_functionCallbacks = [];
		}
		if ($callback === false) {
			static::$_functionResults[$name] = [];
			return static::$_functionCallbacks[$name] = false;
		}
		static::$_functionCallbacks[$name] = $callback;
		if (function_exists($name)) {
			return;
		}

		$function = new ReflectionFunction($callback);
		$pos = strrpos($name, '\\');
		eval(static::_dynamicCode('mockFunction', 'function', [
			'namespace' => substr($name, 0, $pos),
			'function' => substr($name, $pos + 1),
			'args' => static::_methodParams($function),
			'stringArgs' => static::_stringMethodParams($function),
		]));
		return;
	}