public void PutIfAbsent()
        {
            var serdes = new StringSerDes();

            byte[] key3 = serdes.Serialize("key3", new SerializationContext()), value3 = serdes.Serialize("value3", new SerializationContext());

            var store = new InMemoryKeyValueStore("store");

            store.PutIfAbsent(new Bytes(key3), value3);
            store.PutIfAbsent(new Bytes(key3), value3);

            Assert.AreEqual(1, store.ApproximateNumEntries());
        }