clusterresolver: fix a flaky test (#6499)

Author: easwars

xds/internal/balancer/clusterresolver/e2e_test/balancer_test.go

@@ -276,9 +276,11 @@ func (s) TestErrorFromParentLB_ResourceNotFound(t *testing.T) {
 		t.Fatalf("RPCs did not fail after removal of Cluster resource")
 	}
 
-	// Ensure that the ClientConn is in TransientFailure.
-	if state := cc.GetState(); state != connectivity.TransientFailure {
-		t.Fatalf("Unexpected connectivity state for ClientConn, got: %s, want %s", state, connectivity.TransientFailure)
+	// Ensure that the ClientConn moves to TransientFailure.
+	for state := cc.GetState(); state != connectivity.TransientFailure; state = cc.GetState() {
+		if !cc.WaitForStateChange(ctx, state) {
+			t.Fatalf("Timed out waiting for state change. got %v; want %v", state, connectivity.TransientFailure)
+		}
 	}
 
 	// Configure cluster and endpoints resources in the management server.