Composer does not create the top level behat.yml file when installing behat on OS X. This is out of the box for behat ~3.0 for drupal 8.

behat.yml

default:
  suites:
    default:
      contexts:
        - FeatureContext
        - Drupal\DrupalExtension\Context\DrupalContext
        - Drupal\DrupalExtension\Context\MinkContext
        - Drupal\DrupalExtension\Context\MessageContext
        - Drupal\DrupalExtension\Context\DrushContext
  extensions:
    Behat\MinkExtension:
      goutte: ~
      selenium2: ~
      base_url: http://dev.masterd8dev.local.dd:8083
    Drupal\DrupalExtension:
      blackbox: ~
#       api_driver: 'drupal'
#       drupal:
#         drupal_root: '/Users/davmorr/Sites/devdesktop/dev.masterd8dev.local/dev.masterd8dev.local/web'