added grpc_client_low_ut

tests/unit/client/CMakeLists.txt

@@ -97,3 +97,13 @@ add_ydb_test(NAME client-draft_ut
   LABELS
     unit
 )
+
+add_ydb_test(NAME grpc-client-low_ut
+  SOURCES
+  grpc_client_low_ut.cpp
+  LINK_LIBRARIES
+    cpp-testing-unittest_main
+    grpc-client
+  LABELS
+    unit
+)

tests/unit/client/grpc_client_low_ut.cpp

@@ -0,0 +1,61 @@
+#include <ydb-cpp-sdk/library/grpc/client/grpc_client_low.h>
+
+#include <library/cpp/testing/unittest/registar.h>
+
+using namespace NYdbGrpc;
+
+class TTestStub {
+public:
+    std::shared_ptr<grpc::ChannelInterface> ChannelInterface;
+    TTestStub(std::shared_ptr<grpc::ChannelInterface> channelInterface)
+        : ChannelInterface(channelInterface)
+    {}
+};
+
+Y_UNIT_TEST_SUITE(ChannelPoolTests) {
+    Y_UNIT_TEST(UnusedStubsHoldersDeletion) {
+        TGRpcClientConfig clientConfig("invalid_host:invalid_port");
+        TTcpKeepAliveSettings tcpKeepAliveSettings =
+        {
+            true,
+            30, // NYdb::TCP_KEEPALIVE_IDLE, unused in UT, but is necessary in constructor
+            5, // NYdb::TCP_KEEPALIVE_COUNT, unused in UT, but is necessary in constructor
+            10 // NYdb::TCP_KEEPALIVE_INTERVAL, unused in UT, but is necessary in constructor
+        };
+        auto channelPool = TChannelPool(tcpKeepAliveSettings, TDuration::MilliSeconds(250));
+        std::vector<std::weak_ptr<grpc::ChannelInterface>> ChannelInterfacesWeak;
+
+        {
+            std::vector<std::shared_ptr<TTestStub>> stubsHoldersShared;
+            auto storeStubsHolders = [&](TStubsHolder& stubsHolder) {
+                stubsHoldersShared.emplace_back(stubsHolder.GetOrCreateStub<TTestStub>());
+                ChannelInterfacesWeak.emplace_back((*stubsHoldersShared.rbegin())->ChannelInterface);
+                return;
+            };
+            for (int i = 0; i < 10; ++i) {
+                channelPool.GetStubsHolderLocked(
+                    ToString(i),
+                    clientConfig,
+                    storeStubsHolders
+                );
+            }
+        }
+
+        auto now = Now();
+        while (Now() < now + TDuration::MilliSeconds(500)){
+            Sleep(TDuration::MilliSeconds(100));
+        }
+
+        channelPool.DeleteExpiredStubsHolders();
+
+        bool allDeleted = true;
+        for (auto i = ChannelInterfacesWeak.begin(); i != ChannelInterfacesWeak.end(); ++i) {
+            allDeleted = allDeleted && i->expired();
+        }
+
+        // assertion is made for channel interfaces instead of stubs, because after stub deletion
+        // TStubsHolder has the only shared_ptr for channel interface.
+        UNIT_ASSERT_C(allDeleted, "expired stubsHolders were not deleted after timeout");
+
+    }
+} // ChannelPoolTests ut suite