fix flake, avoid panic

xds/internal/balancer/ringhash/e2e/ringhash_balancer_test.go

@@ -208,20 +208,42 @@ func checkRPCSendOK(t *testing.T, ctx context.Context, client testpb.TestService
 	return backendCount
 }
 
+// makeNonExistentBackends returns a slice of e2e.BackendOptions with num
+// listeners, each of which is closed immediately. Useful to simulate servers
+// that are unreachable.
+func makeNonExistentBackends(t *testing.T, num int) []e2e.BackendOptions {
+	closedListeners := make([]net.Listener, 0, num)
+	for i := 0; i < num; i++ {
+		lis, err := testutils.LocalTCPListener()
+		if err != nil {
+			t.Fatalf("testutils.LocalTCPListener() failed: %v", err)
+		}
+		closedListeners = append(closedListeners, lis)
+	}
+
+	// Stop the servers that we want to be unreachable and collect their
+	// addresses.
+	backendOptions := make([]e2e.BackendOptions, 0, num)
+	for _, lis := range closedListeners {
+		backendOptions = append(backendOptions, e2e.BackendOptions{
+			Port:   testutils.ParsePort(t, lis.Addr().String()),
+			Weight: 1,
+		})
+		lis.Close()
+	}
+	return backendOptions
+}
+
 // Tests that when an aggregate cluster is configured with ring hash policy, and
 // the first cluster is in transient failure, all RPCs are sent to the second
 // cluster using the ring hash policy.
 func (s) TestRingHash_AggregateClusterFallBackFromRingHashAtStartup(t *testing.T) {
 	xdsServer, nodeID, _, xdsResolver, stop := e2e.SetupManagementServer(t, e2e.ManagementServerOptions{AllowResourceSubset: true})
 	defer stop()
 
-	nonExistantServers, stopNonExistant := startTestServiceBackends(t, 2)
 	servers, stop := startTestServiceBackends(t, 2)
 	defer stop()
 
-	// Stop the servers that we want to be unreachable.
-	stopNonExistant()
-
 	primaryClusterName := "new_cluster_1"
 	primaryServiceName := "new_eds_service_1"
 	secondaryClusterName := "new_cluster_2"
@@ -233,7 +255,7 @@ func (s) TestRingHash_AggregateClusterFallBackFromRingHashAtStartup(t *testing.T
 		Localities: []e2e.LocalityOptions{{
 			Name:     "locality0",
 			Weight:   1,
-			Backends: backendOptions(t, nonExistantServers),
+			Backends: makeNonExistentBackends(t, 2),
 		}},
 	})
 	ep2 := e2e.EndpointResourceWithOptions(e2e.EndpointOptions{
@@ -336,15 +358,12 @@ func (s) TestRingHash_AggregateClusterFallBackFromRingHashToLogicalDnsAtStartup(
 	backends, stop := startTestServiceBackends(t, 1)
 	defer stop()
 
-	nonExistingBackend, stop1 := startTestServiceBackends(t, 2)
-	stop1()
-
 	endpoints := e2e.EndpointResourceWithOptions(e2e.EndpointOptions{
 		ClusterName: edsClusterName,
 		Localities: []e2e.LocalityOptions{{
 			Name:     "locality0",
 			Weight:   1,
-			Backends: backendOptions(t, nonExistingBackend),
+			Backends: makeNonExistentBackends(t, 1),
 			Priority: 0,
 		}},
 	})
@@ -420,15 +439,12 @@ func (s) TestRingHash_AggregateClusterFallBackFromRingHashToLogicalDnsAtStartupN
 	backends, stop := startTestServiceBackends(t, 1)
 	defer stop()
 
-	nonExistingBackend, stop1 := startTestServiceBackends(t, 2)
-	stop1()
-
 	endpoints := e2e.EndpointResourceWithOptions(e2e.EndpointOptions{
 		ClusterName: edsClusterName,
 		Localities: []e2e.LocalityOptions{{
 			Name:     "locality0",
 			Weight:   1,
-			Backends: backendOptions(t, nonExistingBackend),
+			Backends: makeNonExistentBackends(t, 1),
 			Priority: 0,
 		}},
 	})
@@ -767,9 +783,9 @@ func (s) TestRingHash_HeaderHashingWithRegexRewrite(t *testing.T) {
 //
 // See https://github.com/grpc/grpc/blob/4f6e13bdda9e8c26d6027af97db4b368ca2b3069/test/cpp/end2end/xds/xds_end2end_test_lib.h#L941
 // for an explanation of the formula.
-func computeIdealNumberOfRPCs(p, errorTolerance float64) int {
+func computeIdealNumberOfRPCs(t *testing.T, p, errorTolerance float64) int {
 	if p < 0 || p > 1 {
-		panic("p must be in (0, 1)")
+		t.Fatal("p must be in (0, 1)")
 	}
 	numRPCs := math.Ceil(p * (1 - p) * 5. * 5. / errorTolerance / errorTolerance)
 	return int(numRPCs + 1000.) // add 1k as a buffer to avoid flakyness.
@@ -804,7 +820,7 @@ func setRingHashLBPolicyWithHighMinRingSize(t *testing.T, cluster *v3clusterpb.C
 func (s) TestRingHash_NoHashPolicy(t *testing.T) {
 	backends, stop := startTestServiceBackends(t, 2)
 	defer stop()
-	numRPCs := computeIdealNumberOfRPCs(.5, errorTolerance)
+	numRPCs := computeIdealNumberOfRPCs(t, .5, errorTolerance)
 
 	xdsServer, nodeID, _, xdsResolver, stop := e2e.SetupManagementServer(t, e2e.ManagementServerOptions{AllowResourceSubset: true})
 	defer stop()
@@ -910,7 +926,7 @@ func (s) TestRingHash_EndpointWeights(t *testing.T) {
 	client := testgrpc.NewTestServiceClient(conn)
 
 	// Send a large number of RPCs and check that they are distributed randomly.
-	numRPCs := computeIdealNumberOfRPCs(.25, errorTolerance)
+	numRPCs := computeIdealNumberOfRPCs(t, .25, errorTolerance)
 	gotPerBackend := checkRPCSendOK(t, ctx, client, numRPCs)
 
 	got := float64(gotPerBackend[backends[0].Address]) / float64(numRPCs)