public function fieldValueEquals($field, $value, TraversableElement $container = null)
    {
        $node = $this->fieldExists($field, $container);
        $actual = $node->getValue();
        $regex = '/^'.preg_quote($value, '/').'$/ui';

        $message = sprintf('The field "%s" value is "%s", but "%s" expected.', $field, $actual, $value);

        $this->assert((bool) preg_match($regex, $actual), $message);
    }