behatRadioButtonContext.php

<?php

    /**
    * @Given /^I select the "(?P<field>([^""]|\\")*)" radio button$/
    */
    public function iSelectTheRadioButton($field)
    {
        $field = str_replace('\\"', '"', $field);
        $radio = $this->getSession()->getPage()->findField($field);

        if (null === $radio) {
            throw new ElementNotFoundException(
                $this->getSession(), 'form field', 'id|name|label|value', $field
            );
        }

        $this->fillField($radio->getAttribute('name'), $radio->getAttribute('value'));
    }
    
    // With this in mind:
    $dummy = $this->getSession()->getPage()->find('css', 'label[data-gateway="dummy"] input');
    $this->fillField($dummy->getAttribute('name'), $dummy->getAttribute('value'));