You can’t test it all

By Jim Grey (about)

That new build of software you are about to test? It’s a haystack with some unknown number of needles (bugs) in it.

Hay rolls 3
Have fun finding all the needles!

As a tester, you might think your job is to find all the needles. But how do you do that when you don’t know how many needles are in there? What if there are a lot of needles in there? You’ll never have time to find them all.

You need a plan. You want to find the showstopper bugs right away, and then find as many other bugs that people will care about within the time you have. And then when they come breathing down your neck to stop already and ship, you want to be able to tell them just what badness still might lurk in the code. Give them a reason to think it over.

You do that through assessing risk and targeting test coverage. To assess risk, ask yourself some questions:

  • How stable is the code that was changed? What interactions within the software might these changes break? You’re trying to figure out how likely it is you’ll find bugs.
  • If stuff around these code changes is broken, how much could it hurt the user? How much could it hurt your company? You’re trying to figure out the impact of any bugs you might find.

Risk is the product of likelihood and impact. Test for the highest risk bugs first, working down through the risks. Test more deeply for the bigger risks, more lightly for the smaller ones.

Let’s say they want to ship before you’ve tested through the risks you think people will care about. You can then talk about the risks you haven’t checked for yet, and ask if they’re okay with shipping like that. Do you see the mind shift here? You’re not saying you haven’t run all of your tests yet, which sounds an awful lot like you can’t keep up. Instead, you’re saying that the code might not be ready yet, and here are the specific things you’d like to still check for. It puts you in a much stronger position to get that extra time — and makes it the boss’s decision about what to do next.

Ultimately, it’s best if your developers can and will take great care to not deliver so many needles. That’s always the best case. Click here to read more about it.

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