fix: Flaky test ResolverBadServiceUpdate_NACKedWithoutCache

xds/internal/resolver/helpers_test.go

@@ -28,6 +28,7 @@ import (
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
+
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/grpctest"
@@ -109,16 +110,29 @@ func buildResolverForTarget(t *testing.T, target resolver.Target, bootstrapConte
 		}
 	}
 
-	stateCh := make(chan resolver.State, 1)
+	stateCh := make(chan resolver.State, 10)
 	updateStateF := func(s resolver.State) error {
-		stateCh <- s
+		select {
+		case stateCh <- s:
+		default:
+			select {
+			case <-stateCh:
+				stateCh <- s
+			default:
+			}
+		}
 		return nil
 	}
-	errCh := make(chan error, 1)
+	errCh := make(chan error, 10)
 	reportErrorF := func(err error) {
 		select {
 		case errCh <- err:
 		default:
+			select {
+			case <-errCh:
+				errCh <- err
+			default:
+			}
 		}
 	}
 	tcc := &testutils.ResolverClientConn{Logger: t, UpdateStateF: updateStateF, ReportErrorF: reportErrorF}
@@ -128,7 +142,19 @@ func buildResolverForTarget(t *testing.T, target resolver.Target, bootstrapConte
 	if err != nil {
 		t.Fatalf("Failed to build xDS resolver for target %q: %v", target, err)
 	}
-	t.Cleanup(r.Close)
+	t.Cleanup(func() {
+		go func() {
+			for range stateCh {
+			}
+		}()
+		go func() {
+			for range errCh {
+			}
+		}()
+		r.Close()
+		close(stateCh)
+		close(errCh)
+	})
 	return stateCh, errCh, r
 }