[XdsEnd2endTest] Fix flaky issue 38588

test/cpp/end2end/xds/xds_end2end_test_lib.cc

@@ -399,6 +399,17 @@ XdsEnd2endTest::XdsEnd2endTest(
   default_server_listener_ = XdsResourceUtils::DefaultServerListener();
 }
 
+XdsEnd2endTest::~XdsEnd2endTest() {
+  // We need to make sure that all work from the current test is done before the
+  // next test starts. Without this, we run into errors such as
+  // https://github.com/grpc/grpc/issues/38588. Note that we are using all refs
+  // to current event engine going down to 0 as a proxy for checking that all
+  // work from the current test is done, but this is not a guaranteed way
+  // since there might still be threads that are not using event engine but are
+  // still accessing/modifying the system state.
+  grpc_event_engine::experimental::ShutdownDefaultEventEngine();
+}
+
 void XdsEnd2endTest::TearDown() {
   ShutdownAllBackends();
   balancer_->Shutdown();
@@ -411,6 +422,13 @@ void XdsEnd2endTest::TearDown() {
     remove(bootstrap_file_);
     gpr_free(bootstrap_file_);
   }
+  // Destruct members so that we can make sure no EventEngine ref is being held
+  backends_.clear();
+  stub2_.reset();
+  stub1_.reset();
+  stub_.reset();
+  channel_.reset();
+  balancer_.reset();
 }
 
 std::unique_ptr<XdsEnd2endTest::BalancerServerThread>

test/cpp/end2end/xds/xds_end2end_test_lib.h

@@ -450,6 +450,7 @@ class XdsEnd2endTest : public ::testing::TestWithParam<XdsTestType>,
   // If balancer_credentials is null, it defaults to fake credentials.
   explicit XdsEnd2endTest(
       std::shared_ptr<ServerCredentials> balancer_credentials = nullptr);
+  ~XdsEnd2endTest();
 
   void SetUp() override { InitClient(); }
   void TearDown() override;