def METHOD_NAME():
    client = boto3.client("mq", region_name="us-east-2")
    broker_id = client.create_broker(
        AutoMinorVersionUpgrade=False,
        BrokerName="testbroker",
        DeploymentMode="dm",
        EngineType="ACTIVEMQ",
        EngineVersion="version",
        HostInstanceType="hit",
        PubliclyAccessible=True,
        Users=[],
    )["BrokerId"]
    with pytest.raises(ClientError) as exc:
        client.describe_user(BrokerId=broker_id, Username="unknown")
    err = exc.value.response["Error"]
    assert err["Code"] == "NotFoundException"
    assert (
        err["Message"]
        == "Can't find requested user [unknown]. Make sure your user exists."
    )