/**
 * Create a user with specific roles
 *
 * See http://blog.dcycle.com/blog/45
 *
 * @param $roles
 *   An array of roles by human name, for example, array('administrator', etc.)
 * @param
 *   A Drupal user object.
 *
 * @throws
 *   Exception if undefined roles
 */
public function createUserWithRoles($roles) {
  $user = $this->drupalCreateUser();
  foreach ($roles as $role_name) {
    $role = user_role_load_by_name($role_name);
    if (!$role) {
      throw new Exception('Role ' . $role_name . ' does not seem to be valid; available roles are ' . serialize(user_roles()));
    }
    $user->roles[$role->rid] = $role_name;
  }
  user_save($user);
  return $user;
}