Wednesday, February 20, 2013

A Bug is a Terrible Thing to Waste

Some development teams, especially Agile teams, don’t bother tracking bugs. Instead of using a bug tracking system, when testers find a bug, they talk to the developer and get it fixed, or they write a failing test that needs to be fixed and add it to the Continuous Integration test suite, or if they have to, they write up a bug story on a card and post it on the wall so the team knows about it and somebody will commit to fixing it.

Other teams live by their bug tracking systems, using tools like Jira or Bugzilla or FogBugz to record bugs as well as changes and other work. There are arguments to be made for both of these approaches.

Arguments for tracking bugs – and for not tracking bugs

In Agile Testing: A Practical Guide for Testers and Agile Teams, Lisa Crispin and Janet Gregory examine the pros and cons of using a defect tracking system.

Using a system to track bugs can be the only effective way to manage problems for teams who can’t meet face-to-face - for example, distributed teams spread across different time zones. It can also be useful for teams who have inherited open bugs in a legacy system; and a necessary evil for teams who are forced to track bugs for compliance reasons. The information in a bug database is a potential knowledge base for testers and developers joining the team – they can review bugs that were found before in the area of the code that they are working on to understand what problems they should look out for. And bug data can be used to collect metrics and create trends on bugs – if you think that bug metrics are useful.

But the Lean/Agile view is that using a defect tracking system mostly gets in the way and slows people down. The team should stay focused on finding bugs, fixing them, and then forget about them. Bugs are waste, and everything about them is waste – dead information, and dead time that is better spent delivering value. Worse, using a defect tracking system prevents testers and developers from talking with each other, and encourages testers to take a “Quality Police” mindset. Without a tool, people have to talk to each other, and have to learn to play nicely together.

This is a short-term, tactical point of view, focused on what is needed to get the software out the door and working. It’s project-thinking, not product thinking.

Bugs over the Long Term

But if you’re working on a system over a long time like we are, if you're managing a product or running a service, you know that it’s not that simple. You can’t just look at what’s in front of you, and where you want to be in a year or more. You also have to look back, at the work that was done before, at problems that happened before, at decisions that were made before, to understand why you are where you are today and where you may be heading in the future.

Because some problems never go away. And other problems will come back unless you do something to stop it. And you’ll find out that other problems which you thought you had licked never really went away. The information from old bugs, what happened and what somebody did to fix them (or why they couldn't fix them), which workarounds worked (and which didn't) can help you understand and deal with the problems that you are seeing today, and help you to keep improving the system and how you build it and keep it running.

Because you should understand the history of changes and fixes to the code if you’re going to change it. If you like the way the code is today, you might want to know how and why it got this way. If you don’t like it, you’ll want to know how and why it got this way – it’s arrogant to assume that you won’t make the same mistakes or be forced into the same kinds of situations. Revision control will tell you what was changed and when and who did it, the bug tracking system will tell you why.

Because you need to know where you have instability and risk in the system. You need to identify defect-dense code or error-prone code – code that contains too many bugs, code that is costing you too much to maintain and causing too many problems, code that is too expensive to keep running the way that is today. Code that you should rewrite ASAP to improve stability and reduce your ongoing costs. But you can’t identify this code without knowing the history of problems in the system.

Because you may need to prove to auditors or regulators and customers and investors that you are doing a responsible job of testing and finding bugs and fixing them and getting the fixes out.

And because you want to know how effective the team is in finding, fixing and preventing bugs. Are you seeing fewer bugs today? Or more bugs? Are you seeing the same kinds of bugs – are you making the same mistakes? Or different mistakes?

Do you need to track every Bug?

As long as bugs are found early enough, there’s little value in tracking them. It’s when bugs escape that they need to be tracked: bugs that the developer didn't find right away on their own, or in pairing, or through the standard automated checks and tests that are run in Continuous Integration.

We don’t log

  • defects found in unit tests or other automated tests – unless for some reason the problem can’t or won’t be fixed right away;
  • problems found in peer reviews – unless something in the review is considered significant and can’t get addressed immediately. Or a problem is found in a late review, after testing has already started, and the code will need to be retested. Or the reviewer finds something wrong in code that wasn't changed, an old bug – it’s still a problem that needs to be looked at, but we may not be prepared to deal with it right now. All problems found in external reviews, like a security review or an audit, are logged;
  • static analysis findings – most of the problems caught by these tools are simple coding mistakes that can be seen and fixed right away, and there’s also usually a fair amount of noise (false positives) that has to be filtered out. We run static analysis checks and review them daily, and only log findings if we agree that the finding is real but the developer isn't prepared to fix it immediately (which almost never happens, unless we’re running a new tool against an existing code base for the first time). Many static analysis tools have their own systems for tracking static analysis findings any ways, so we can always go back and review outstanding issues later;
  • bugs found when developers and testers decide to pair together to test changes early in development, when they are mostly exploring how something should work – we don’t usually log these bugs unless they can’t be / won’t be fixed (can’t be reproduced later for example).

A Bug is a Terrible thing to Waste

We log all other bugs regardless of whether they are found in production, in internal testing, partner testing, User Acceptance Testing, or external testing (such as a pen test). Because most of the time, when software is handed to a tester, it’s supposed to be working. If the tester finds bugs, especially serious ones, then this is important information to the tester, to the developer, and to the rest of the team. It can highlight risks. It can show where more testing and reviews need to be done. It can highlight deeper problems in the design, a lack of understanding that could cause other problems.

If you believe that testing provides important information not just about the state of your software, but also on how you are designing and building it – then everyone needs to be able to see this information, and understand it over time. Some problems can’t be seen or fully understood right away, or in 1-week or 2-week sprint-sized chunks. It can take a while before you recognize that you have a serious weakness in the design or that something is broken in your approach to development or in your culture. You’ll need to experience a few problems before you start to find relationships between them and before you can look for their root cause. You’ll need data from the past in order to solve problems in the future.

Tracking bugs isn't a waste if you learn from bugs. Throwing the information on bugs away is the real waste.


Unknown said...

Great post!

I agree with you that keeping track on bugs is realy valuable. Some part of your code are more error prone than others. Bugs come and go over time, but in another form. Some bugs arises from fixes from old bugs, that are fixes for even older bugs.
It is the really valuable to have access to this history.

I work at Ericsson, on of the largets telecommunication company in the world, were the oldest code is more than 20 years old (I'm talking about the GSM network). Some error reports from our customers are on features that were developed years ago. Some years later a customer reportes a in the same area which reminds of the old on.

History for us is very importand!

Jim Bird said...


Thank you. I can see why bug history would be very important for you - and valuable. It's good to hear from someone with your experience, and it's good to see software that is 20 years or more old that is still important and still being actively worked on.

I thought of another case where tracking bugs is important, when you have different versions of the same software out to different customers, which of course happens at many product companies. Tracking what version the bug was found in, which versions need to be fixed (and whether the fix needs to be different for different versions), which have been fixed, when the fix was made, what customers have received the fix - all of this is critical to keeping a product working.

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