fix edge case in test

Author: s-matyukevich

balancer/deterministicsubsetting/balancer.go

@@ -90,7 +90,7 @@ func (b *subsettingBalancer) prepareChildResolverState(s resolver.State) resolve
 	excludedCount := backendCount % int(b.cfg.SubsetSize)
 	excludedStart := (round * excludedCount) % backendCount
 	excludedEnd := (excludedStart + excludedCount) % backendCount
-	if excludedStart < excludedEnd {
+	if excludedStart <= excludedEnd {
 		addresses = append(addresses[:excludedStart], addresses[excludedEnd:]...)
 	} else {
 		addresses = addresses[excludedEnd:excludedStart]

balancer/deterministicsubsetting/e2e_test/subsetting_test.go

@@ -141,6 +141,8 @@ func checkRoundRobinRPCs(t *testing.T, ctx context.Context, clients []testgrpc.T
 				} else {
 					m[clientIdx] = struct{}{}
 				}
+			} else {
+				t.Fatalf("peer.Addr == nil, peer: %v", peer)
 			}
 		}
 	}