{Address: "1.2.3.4", Port: 82, Protocol: simulation.TCP, HostHeader: "headless.default.svc.cluster.local"},

		// Use short host name
		{Address: "1.2.3.4", Port: 83, Protocol: simulation.TCP, TLS: simulation.TLS, HostHeader: "headless.default"},
		{Address: "1.2.3.4", Port: 84, Protocol: simulation.HTTP, TLS: simulation.TLS, HostHeader: "headless.default"},
	} {

		}
		// headless service update must trigger nds push, so we trigger a full push.
		if ev := fx.WaitOrFail(t, "xds full"); !ev.Reason.Has(model.HeadlessEndpointUpdate) {
			t.Fatalf("xds push reason does not contain %v: %v", model.HeadlessEndpointUpdate, ev)
		}

		// pure HTTP headless services should not need a full push since they do not

	// a workload that backs a Kubernetes service will typically have only endpoints. A
	// workload that backs a headless Kubernetes service, however, will have both
	// addresses as well as a hostname used for direct access to the headless endpoint.
	// TODO: support this field
	Hostname string `protobuf:"bytes,21,opt,name=hostname,proto3" json:"hostname,omitempty"`

	fx.WaitOrFail(t, "eds")

	// delete normal service
	clienttest.Wrap(t, controller.services).Delete("svc1", "nsa")
	fx.WaitOrFail(t, "service")

	// 2. full xds push request for headless service endpoint update

	// create a headless service
	createServiceWithoutClusterIP(controller, "svc1", "nsa", nil,
		[]int32{8080}, map[string]string{"app": "prod-app"}, t)
	fx.WaitOrFail(t, "service")

const (
	// EndpointUpdate describes a push triggered by an Endpoint change
	EndpointUpdate TriggerReason = "endpoint"
	// HeadlessEndpointUpdate describes a push triggered by an Endpoint change for headless service
	HeadlessEndpointUpdate TriggerReason = "headlessendpoint"
	// ConfigUpdate describes a push triggered by a config (generally and Istio CRD) change.
	ConfigUpdate TriggerReason = "config"

- Services implement a field selector for the ClusterIP and Type fields.
  Kubelet uses the fieldselector on Services to avoid watching for Headless Services and reduce the memory consumption. ([#123905](https://github.com/kubernetes/kubernetes/pull/123905), [@aojea](https://github.com/aojea)) [SIG Apps, Node and Testing]

  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: {{.Resolution}}
  location: {{.Location}}
  endpoints:
  # we send directly to a Pod IP here. This is essentially headless
  - address: {{.IngressIp}} # TODO won't work with DNS resolution tests
    ports:
      http: {{.IngressHttpPort}}`).
				WithParams(param.Params{}.SetWellKnown(param.Namespace, apps.Namespace))

	T := pkg.Scope().Lookup("T").Type().(*Named)
	if n := T.TypeParams().Len(); n != 1 {
		t.Fatalf("expected 1 type parameter; found %d", n)
	}

	// instantiation should succeed (no endless recursion)
	// even with a nil *Checker
	res, err := Instantiate(nil, T, []Type{Typ[Int]}, false)
	if err != nil {
		t.Fatal(err)
	}

	// instantiated type should point to itself