Adds a given user to given group as given role.

add_member_to_group.txt

/**
 * Adds a given user as member with given role to given group.
 * @param GroupInterface $group
 *  Group Entity
 * @param UserInterface $user
 *  An user account entity of type User Interface , not of Account Interface.
 * @param array $role
 *  A group role in format : [GROUPTYPE]-[role] Ex: group-teacher
 */
function add_member_to_group(GroupInterface $group, UserInterface $user, $role) {
  // For multiple roles, ['group_roles' => ['role1', 'role2']].
  $roles = ['group_roles' => $role];
  $group->addmember($user, $roles);
}