Code coverage goal: 80% and no less!

by Alberto Savoia

I first posted this article a few years ago on the Artima Developer website; but the question of what's adequate code coverage keeps coming up, so I thought it was time for a repost of Testivus wisdom on the subject.

Testivus on Test Coverage

Early one morning, a young programmer asked the great master:

“I am ready to write some unit tests. What code coverage should I aim for?”

The great master replied:

“Don’t worry about coverage, just write some good tests.”

The young programmer smiled, bowed, and left.

Later that day, a second programmer asked the same question.

The great master pointed at a pot of boiling water and said:

“How many grains of rice should I put in that pot?”

The programmer, looking puzzled, replied:

“How can I possibly tell you? It depends on how many people you need to feed, how hungry they are, what other food you are serving, how much rice you have available, and so on.”

“Exactly,” said the great master.

The second programmer smiled, bowed, and left.

Toward the end of the day, a third programmer came and asked the same question about code coverage.

“Eighty percent and no less!” Replied the master in a stern voice, pounding his fist on the table.

The third programmer smiled, bowed, and left.

After this last reply, a young apprentice approached the great master:

“Great master, today I overheard you answer the same question about code coverage with three different answers. Why?”

The great master stood up from his chair:

“Come get some fresh tea with me and let’s talk about it.”

After they filled their cups with smoking hot green tea, the great master began:

“The first programmer is new and just getting started with testing. Right now he has a lot of code and no tests. He has a long way to go; focusing on code coverage at this time would be depressing and quite useless. He’s better off just getting used to writing and running some tests. He can worry about coverage later.

The second programmer, on the other hand, is quite experienced both at programming and testing. When I replied by asking her how many grains of rice I should put in a pot, I helped her realize that the amount of testing necessary depends on a number of factors, and she knows those factors better than I do – it’s her code after all. There is no single, simple, answer, and she’s smart enough to handle the truth and work with that.”

“I see,” said the young apprentice, “but if there is no single simple answer, then why did you tell the third programmer ‘Eighty percent and no less’?”

The great master laughed so hard and loud that his belly, evidence that he drank more than just green tea, flopped up and down.

“The third programmer wants only simple answers – even when there are no simple answers … and then does not follow them anyway.”

The young apprentice and the grizzled great master finished drinking their tea in contemplative silence.

Permalink | Links to this post | 19 comments  

There, but for the grace of testing, go I

By James A. Whittaker

I've had more than a few emails about "antenna-gate" asking me to comment and suggesting clever, stabbing rebukes to a fallen competitor. I might aim a few of those at my own team in the future, some were genuinely funny, but none of them will appear here. Instead I offer first a word of caution and second a reflection that my Mom used to intone whenever disaster occurred around her. It's called "counting your blessings."

First, a caution that those of us who live in glass houses really should keep stones at arms length. The only way anyone can rebuke Apple, without risk of waking up one morning sucking on their own foot, is if they write no software or have no users. Apple does a lot of the former and they enjoy many of the latter. Bugs like this make me sick when they are mine and nervous when they aren't. If any tester in the industry isn't taking stock right now then they either aren't producing any software or aren't in possession of any users, at least ones they wish to keep.

Second, taking stock has made me realize that I enjoy some important blessings that make the infinite task of testing so much more manageable. Indeed, the three blessings I count here are really the reason that testing doesn't fail more often than it does.

The Blessing of Unit Testing

I am thankful for early cycle testing thinning out the bug herd. In late cycle testing major bugs are often masked by minor bugs and too many of the latter can hamper the search for the former. Every bug that requires a bug report means lost time. There is the time spent to find the bug; time spent to reproduce and report it; time to investigate its cause and ensure it is not a duplicate; time to fix it, or to argue about whether it should be fixed; time to build the new version and push it to the test lab; time to verify the fix; time to test that the fix introduced no additional bugs. Clearly the smaller the population to begin with, the easier the task becomes. Solid unit testing is a tester's best friend.

The Blessing of Rarity

I am thankful that the vast majority of bugs that affect entire user populations are generally nuisance-class issues. These are typically bugs concerning awkward UI elements or the occasional misfiring of some feature or another where workarounds and alternatives will suffice until a minor update can be made. Serious bugs tend to have a more localized effect. True recall class bugs, serious failures that affect large populations of users, are far less common. Testers can take advantage of the fact that not all bugs are equally damaging and prioritize their effort to find bugs in the order of their seriousness. The futility of finding every bug can be replaced by an investigation based on risk.

Risk analysis is so important that we've built an internal tool to help guide testers in performing it. Code-named "Testify" this tool streamlines the process of risk analysis, at least the way we do it at Google. We're working on open-sourcing an early prototype in time for GTAC 2010 (I can hear my team cringing now ... "you promised it when?").

The Blessing of Repetition

I am thankful that user behavior is highly repetitive. There are features that enjoy heavy usage across user populations and features that are far less popular. Mobile phones are a good example of this. The phone is constantly establishing connections to networks. Certain features like making and receiving calls, texting and so forth are used more often than taking pictures or searching maps. The popularity of user applications is a matter of hard data, not guesswork. Knowing what users do most often, less often and least often means testing resources can be applied with a commensurate amount of force and that testing itself can be patterned after actual usage profiles.

Testers can gain a great deal from taking the user’s point of view and weaving usage concerns into the software testing process. Focusing on the user ensures that high impact bugs are found early and software revisions that break key user scenarios are identified quickly and not allowed to persist.

Apple may be the company in the news today, who knows who it will be tomorrow. Every company that produces software people care about has either been there or will be there. The job is simply too big for perfection to be an option. But there are key advantages we have that make the job manageable.

Put down the stones and make sure that what few blessing we testers possess are being exploited for everything they are worth. Hopefully, your company will be spared and the next time a company suffers such a bug you won't be the one making excuses. Perhaps you'll be lucky enough to be the one saying, "there but for the grace of testing go I."

Permalink | Links to this post | 11 comments  

Testivus, Testability and Dr. Jekyll and Mr. Hyde

by Alberto Savoia

Note: Apparently, there were lots of downloads of the Testivus booklet and I hit some kind of quota on my personal account. If you have problems with reaching the original link below, please try this new download link or this one.

A major topic at this year's GTAC conference is going to be testability: "We also want to highlight methodologies and tools that can be used to build testability into our products." That's great!

Testability is one of the most important, yet overlooked, attributes of code – and one that is not discussed enough. That's unfortunate, because by the time the issue of testability comes up in a project it's usually too late. As preparation and seeding for GTAC, I though it would be fun and useful to get some discussions on testability going. So here we go, feel free to chime in with your thoughts.

A few years ago, after watching one too many episodes of Kung Fu, I was inspired to write a pretentious and cryptic little booklet about testing called "The Way of Testivus" (PDF).

Testivus addresses the issue of testability in a few places, but I would like to start the discussion with this maxim:

To me, "Think of code and tests as one" is the very foundation of testability. If you don't think about testing as you design and implement your code, you are very likely to make choices that will impair testability when the time comes. This position seemed obvious and non-controversial to me at the time I wrote it, and I still stand by it. Most people seem to agree with it as well, and more than one person told me that it's their favorite and most applicable maxim from all of Testivus. There are however three groups of people who found issue with it.

Some of the people, mostly from the TDD camp, think that my choice of words leaves too much wiggle room: "Thinking about the tests is not enough, they should be writing and running those tests at the same time."

Others think that code and tests should not be thought of as one at all, but they should be treated independently – ideally as adversaries: "I don't want code and tests to be too "friendly". Production code should not be changed or compromised to make the testing easier, and tests should not trust the hooks put in the code to make it more testable." Most of the people in this camp are not big fans of unit/developer testing in the first place, but not all. One person, a believer in developer testing, told me that he gets the best results with a Dr. Jekyll and Mr. Hyde approach. He assumes two different roles and personalities based on whether he's coding or testing his own code. When coding, he's the constructive Dr. Jekyll who focuses on elegant and efficient design and algorithms – and does not worry about testability. When testing, he turns into the destructive Mr. Hyde; he tries to forget that it's his code or how he implemented it, and puts all his energy and anger into trying to break it. Sounds like it could work quite well – though I don't think I'd want this person as an office mate during the Mr. Hyde phase.

A third group, thought that the maxim was fine for unit tests, but not applicable to other types of tests that were best served by an adversarial black-box approach.

What are your thoughts? Is it enough to think about testability when designing or writing the code, or must you actually write and run some tests in parallel with the code? Does anyone agree with the position that code and tests should be designed and developed in isolation? Are there other Dr. Jekylls and Mr. Hydes out there?

Alberto

Permalink | Links to this post | 14 comments