ringhash: Replace DNS resolver before sending xDS Update in test (#8091)

Author: arjan-bal

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

@@ -467,13 +467,14 @@ func (s) TestRingHash_AggregateClusterFallBackFromRingHashToLogicalDnsAtStartup(
 		Routes:    []*v3routepb.RouteConfiguration{route},
 		Listeners: []*v3listenerpb.Listener{listener},
 	}
-	if err := xdsServer.Update(ctx, updateOpts); err != nil {
-		t.Fatalf("Failed to update xDS resources: %v", err)
-	}
 
 	dnsR := replaceDNSResolver(t)
 	dnsR.InitialState(resolver.State{Addresses: []resolver.Address{{Addr: backends[0]}}})
 
+	if err := xdsServer.Update(ctx, updateOpts); err != nil {
+		t.Fatalf("Failed to update xDS resources: %v", err)
+	}
+
 	conn, err := grpc.NewClient("xds:///test.server", grpc.WithResolvers(xdsResolver), grpc.WithTransportCredentials(insecure.NewCredentials()))
 	if err != nil {
 		t.Fatalf("Failed to create client: %s", err)
@@ -544,13 +545,14 @@ func (s) TestRingHash_AggregateClusterFallBackFromRingHashToLogicalDnsAtStartupN
 		Routes:    []*v3routepb.RouteConfiguration{route},
 		Listeners: []*v3listenerpb.Listener{listener},
 	}
-	if err := xdsServer.Update(ctx, updateOpts); err != nil {
-		t.Fatalf("Failed to update xDS resources: %v", err)
-	}
 
 	dnsR := replaceDNSResolver(t)
 	dnsR.InitialState(resolver.State{Addresses: []resolver.Address{{Addr: backends[0]}}})
 
+	if err := xdsServer.Update(ctx, updateOpts); err != nil {
+		t.Fatalf("Failed to update xDS resources: %v", err)
+	}
+
 	dialer := testutils.NewBlockingDialer()
 	cp := grpc.ConnectParams{
 		// Increase backoff time, so that subconns stay in TRANSIENT_FAILURE