public void When()
        {
            _tagger = new StreamPositionTagger("stream1");
            _positionTracker = new PositionTracker(_tagger);
            // when

            _positionTracker.UpdateByCheckpointTagInitial(_tagger.MakeZeroCheckpointTag());
        }
        public void produced_checkpoint_tags_are_correctly_ordered()
        {
            var t = new StreamPositionTagger("stream1");
            var zero = t.MakeZeroCheckpointTag();

            var zeroEvent = t.MakeCheckpointTag(zero, _zeroEvent);
            var zeroEvent2 = t.MakeCheckpointTag(zeroEvent, _zeroEvent);
            var first = t.MakeCheckpointTag(zeroEvent2, _firstEvent);
            var second = t.MakeCheckpointTag(first, _secondEvent);
            var second2 = t.MakeCheckpointTag(zero, _secondEvent);

            Assert.IsTrue(zeroEvent > zero);
            Assert.IsTrue(first > zero);
            Assert.IsTrue(second > first);

            Assert.AreEqual(zeroEvent2, zeroEvent);
            Assert.AreEqual(second, second2);
        }
        public void zero_position_tag_is_before_first_event_possible()
        {
            var t = new StreamPositionTagger("stream1");
            var zero = t.MakeZeroCheckpointTag();

            var zeroFromEvent = t.MakeCheckpointTag(zero, _zeroEvent);

            Assert.IsTrue(zeroFromEvent > zero);
        }