errFatal := func(err error) {
		b.Helper()
		if err != nil {
			b.Fatal(err)
		}
	}
	rpc := NewSingleHandler[*testRequest, *testResponse](handlerTest2, newTestRequest, newTestResponse)
	grid, err := SetupTestGrid(n)
	errFatal(err)
	b.Cleanup(grid.Cleanup)
	// Create n managers.
	for _, remote := range grid.Managers {
		// Register a single handler which echos the payload.

	Managers    []*Manager
	Mux         []*mux.Router
	Hosts       []string
	cleanupOnce sync.Once
	cancel      context.CancelFunc
}

// SetupTestGrid creates a new grid for testing purposes.
// Select the number of hosts to create.
// Call (TestGrid).Cleanup() when done.
func SetupTestGrid(n int) (*TestGrid, error) {
	hosts, listeners, err := getHosts(n)
	if err != nil {
		return nil, err
	}
	dialer := &net.Dialer{

)

func TestSingleRoundtrip(t *testing.T) {
	defer testlogger.T.SetLogTB(t)()
	errFatal := func(err error) {
		t.Helper()
		if err != nil {
			t.Fatal(err)
		}
	}
	grid, err := SetupTestGrid(2)
	errFatal(err)
	remoteHost := grid.Hosts[1]
	local := grid.Managers[0]

	// 1: Echo
	errFatal(local.RegisterSingleHandler(handlerTest, func(payload []byte) ([]byte, *RemoteErr) {