--- FAIL: TestClientTTRPC_Close (0.00s)
    client_ttrpc_test.go:70: assertion failed: rpc error: code = InvalidArgument desc = event envelope has invalid namespace: namespace "" must match ^[A-Za-z][A-Za-z0-9]+(:?[-]+[A-Za-z][A-Za-z0-9]+)*(?:[.](?:[A-Za-z][A-Za-z0-9]+(:?[-]+[A-Za-z][A-Za-z0-9]+)*))*$: invalid argument (err *status.statusError) != ttrpc: closed (ttrpc.ErrClosed *errors.fundamental)

# vendor/github.com/containerd/ttrpc/client.go
for {
                select {
                case call := <-calls:
                        if err := c.send(call.ctx, streamID, messageTypeRequest, call.req); err != nil {
                                call.errs <- err
                                continue
                        }

                        waiters[streamID] = call
                        streamID += 2 // enforce odd client initiated request ids
                case msg := <-incoming:
                        call, ok := waiters[msg.StreamID]
                        if !ok {
                                logrus.Errorf("ttrpc: received message for unknown channel %v", msg.StreamID)
                                continue
                        }

                        call.errs <- c.recv(call.resp, msg)
                        delete(waiters, msg.StreamID)
                case <-shutdown:
                        if shutdownErr != nil {
                                shutdownErr = filterCloseErr(shutdownErr)
                        } else {
                                shutdownErr = ErrClosed
                        }

                        shutdownErr = errors.Wrapf(shutdownErr, "ttrpc: client shutting down")

                        c.err = shutdownErr
                        for _, waiter := range waiters {
                                waiter.errs <- shutdownErr
                        }
                        c.Close()
                        return
                case <-c.closed:
                        if c.err == nil {
                                c.err = ErrClosed
                        }
                        // broadcast the shutdown error to the remaining waiters.
                        for _, waiter := range waiters {
                                waiter.errs <- c.err
                        }
                        return
 }