Let's assume that part of the story (worth say 8 points) was done in the sprint 1.
Then, after implementing part of it we are discovering that in fact it is much bigger than originally estimated. Credit for completing the story was not given in sprint 1 (story was not completed) and it was moved back to product backlog.
- Now, should we re-estimate it during the planning for sprint 2?
- Should the estimate contain ONLY remaining part of the story (part was already done in sprint 1) or the total size of the story (then implemented part should be reflected in team capacity so that more stories will be taken to the next sprint)?
If we use the later approach what with other stories which are there in the product backlog and were estimated based on the story which was re-estimated (aka the size of this next story was similar to the one that was re-estimated and that's why next story has some particular size). Should we change estimates of all such a stories as well? This seem to be quite a big overhead.
If we use the first one then we know straight from the beginning that our velocity current sprint (sprint 2) will be much lower than usual as the story is having inaccurate estimate (and we already know it during the planning).
What should be the best approach here?
To clarify what I mean by re-estimating. I don't want to move only part of the work which was not done to the next sprint, but in fact we've figured out that our original estimate was wrong. Should we so to say change the estimate to 21 instead of 8 and agree that half was done in sprint 1 and we will have to spent time needed to develop remaining 10-11 story points in the next sprint (sprint 2)?