public void update_custom_data()
{
_writer.Create(_documentHandle);
var handleCustomData = new DocumentCustomData()
{
{ "a", "b" }
};
_writer.UpdateCustomData(_documentHandle, handleCustomData);
var h = _writer.FindOneById(_documentHandle);
Assert.NotNull(h.CustomData);
Assert.AreEqual("b", (string)h.CustomData["a"]);
}