Disable buggy tests

paddle/fluid/operators/detail/grpc_server_test.cc

@@ -108,7 +108,10 @@ void StartServer(const std::string& endpoint) {
   rpc_service_->RunSyncUpdate();
 }
 
-TEST(PREFETCH, CPU) {
+// NOTE(yuyang18) : This test is buggy.
+// 1. We should not use port 8889 before check.
+// 2. We should not use sleep(2) to sync threads.
+TEST(PREFETCH, DISABLE_CPU) {
   // start up a server instance backend
   std::thread server_thread(StartServer, "127.0.0.1:8889");
   sleep(2);

python/paddle/fluid/tests/unittests/test_dist_train.py

@@ -25,6 +25,9 @@ import time
 
 
 class TestSendOp(unittest.TestCase):
+    @unittest.skip(
+        "This test is buggy. We cannot use time.sleep to sync processes, the connection may fail in unittest."
+    )
     def test_send(self):
         # Run init_serv in a thread
         place = fluid.CPUPlace()