There's a guiding principle that everyone should apply - "Bug driven development is evil". But it's common. And bugs on the backlog are a varient of bug driven development.




Why is it evil? Because bugs are impossible to estimate. OK, maybe impossible is too strong, but I'd argue that "several orders of maginitude harder to estimate than features" is accurate. If you plan your project using a list of bugs then your estimated timescales are going to be utterly useless.




What's the antidote? What's the opposite of "bug driven development"? It's much easier to estimate how long it will take to test something than it is to estimate how long it will take to fix bugs in it. So if you've got high priority bugs that have escaped the sprint then put tests for them on the backlog. It's not the conventional meaning of "test driven development", but it works for me.




Piers

So far so good - what happens if many low priority bugs are found? Do you fix them in preference to doing work that the PO wants?

#, First, to reiterate, do everything you can to never let the code leave the developers desk with bugs. Duh.



Second, if you find it during the iteration, fix it. Verbal communication to coordinate this is best.



Finally, if it's found post iteration - fix it somewhere between "now" and "first thing next iteration" (at the latest), favoring "now" whenever possible, depending on the criticality of the bug.



Consider this: if you could have predicted the bug when you first slated the story for development, would you ever have considered prioritizing that bug for "sometime later"? Of course not, you'd have demanded the bug never make it in. Why allow a different attitude when the bug comes in later?



Bottom line, keeping growing repositories of bugs (whether in bug trackers or backlogs) is a bane to productivity. Make it a top priority to avoid.



Cheers,

MB

#, What does "low priority bug" really mean?



My take is this: if you have a "bug", meaning the software aint doing what was expected, then it either gets fixed ASAP (see my other response), or it's not a "bug". If it can "prioritized for later", then it becomes a real-deal story.

So far so good - but do you ask why the bug was written in the first place? Your doing well the challenge is always about getting to the next stage.

I think this approach is on the money and in the long run you will have as George said "vanishingly few bugs". Most teams I see shy away from this approach saying but we will never get any work on features done. Sad. Keep at this Anton you're going in the right direction.

#, ..and, yes, for any bug - inspect (into why it occurred) and adapt.

I agree with the ones of you guys saying, that bugs should never escape the developers during a sprint, as long as we are talking green field projects, or at least projects that has been running scrum from the beginning.

In "brown field" projects, and projects having recently made the switch from something else to scrum, it's a very different ball game.

Typically projects like that are blessed with a large number of known bugs, and perhaps even more unknown ones. Bug tracking systems are often in place, and the customer is acustomed to discovering new bugs within every release. Unit tests are absent or at least way too few, and testers are often a scarce resource, so it's only on rare occasions, that the entire system is tested properly.

On projects like these, it is often not feasible to have a strategy to fix a bug as soon as it is found, because of the hard-to-estimate nature of bugs - the team will not get any features "done" in the sprint.

If the customer is paying per implemented feature, and not for bug fixes, it actually works quite well to treat bugs as "features with negative value", as Kevlin puts it. That way the customer can prioritize wether to have the team focusing on stabilizing the product or adding new functionality.

I would strongly recommend teams on projects like this apply the techniques explained by Michael Feathers in the book "Working Effectively with Legacy Code", so the code coverage of the system increases sprint by sprint.

Just my humble opinion :-)

Sorry, this was my first post in here, and my formatting of the message went poof ...

By the way we have a joke with my colleague "If you want to write software do it at home not in the office!". The reason is that nobody wants to invest time in what ever activity which doesn't return value now ! ;-)

Legacy code is only a bit different. My focus never make the situation worse, always try to make it a bit better. In this case I would suggest no new bugs should escape the sprint.

As to the Michael Feathers recommendation "Working Effectively with Legacy Code" - I second it.

You hit the nail on the head. This is the first question you must ask... is it a bug, or is it a change? I've seen a lot of bugs that have come up that were "We asked you for x, never thinking about y, so could you please change the system so that y is covered?" It's a business scenario, so there's little reason to expect a dev or tester to anticipate/test it.
I know where we've struggled is in injecting items into the product backlog, we tend to classify it as a bug and so we end up with a lot of bugs, but not a lot of change in the back log. That's exactly what I think we're supposed to be avoiding in Scrum or any other agile methodology. As we see change, we should be taking it on as a feature and prioritizing it accordingly. Only when it's something broken should it be called a bug.

Precisely.

At my last company, we took the following approach (the app was a single-instance SaaS serving about 2.2 million K-8 students and their teachers):

• * Each release (approx 3-4 2-week sprints) a team member was assigned to the 3rd-level support role. The rest of the team focused solely on the current release.
  


• * The person assigned to 3rd level support was permitted to work on applied R&D projects of his/her choosing that we agreed were worthwhile to the company. You can think of these as "spikes" to increase stored value in using new technology we were considering to solve problems further out on the roadmap. Sometimes it was simply paying down any "technology debt" that had accrued.
  


• * These projects had to be shelved immediately if any defects appeared in production and were affecting customers. The person was permitted to spend up to one day without prior approval from the product owner. During that time if it couldn't be solved it had to be characterized via a clear test case and an estimate on how it impacted customers. The product manager could decide whether it became a story or whether the person doing 3rd level support could continue for a bit longer.
  


• * Fixing the bug included identifying whether the defect was based on fragile architecture, insufficient testing, or imperfect understanding of what the customer's expectations would be. (When you have a large customer base, you find folks who use the product in a way that doesn't match the original scenarios.)
  

Wow Doug - I think you've found a great approach to this problem. You've also identified the biggest weakness that I can see.

One shouldn't classify things into bugs vs features, in first place. It leads to wasted time spent arguing whether something is a bug or not, make people feel and treat them differently, and is awkward to manage, as, after all, it takes exactly the same work to do either.

What exists is an unsatisfied requirement. If the user says the requirement is part of something that was already done, then you pick the whole story, bring it back to the product backlog, do whatever further detail the team thinks necessary -- if they think it necessary, and prioritize it right along everything else.

That gets rid of the blame game, focus on the fact that the requisite is not "done", and makes it possible to prioritize workload appropriately.

Now, if that is not viable because the contract says bug correction is free, everything else is not, then you have a bad contract. Instead of trying to get someone else to pay up for badly written software -- since you'll not get that anyway, the price tag will just be added to other expenses one way or another -- you should focus on getting good developers, good tools and good process.