def METHOD_NAME(ret, ruby, user=None):
    """
    Check to see if given ruby is installed.
    """
    default = __salt__["rbenv.default"](runas=user)
    for version in __salt__["rbenv.versions"](user):
        if version == ruby:
            ret["result"] = True
            ret["comment"] = "Requested ruby exists"
            ret["default"] = default == ruby
            break
    return ret