PhpSpec\Console\Application::ensureIsValidMatcherClass PHP Method

    private function ensureIsValidMatcherClass($class)
    {
        if (!class_exists($class)) {
            throw new InvalidConfigurationException(sprintf('Custom matcher %s does not exist.', $class));
        }
        if (!is_subclass_of($class, Matcher::class)) {
            throw new InvalidConfigurationException(sprintf('Custom matcher %s must implement %s interface, but it does not.', $class, Matcher::class));
        }
    }