We’ve been interviewing to fill a couple QA positions on our team. My favorite part of each interview is my “test this light switch” exercise. It reveals interesting skills about each test candidate.

I point to the light switch in the room and say “test this light switch”. Here is a sampling of how candidates have responded:

  • some asked if there are any requirements (this is a great way to start!)
  • some just start testing with lots of assumptions (no so great)
  • one candidate smiled and thought I was kidding. After asking lots of questions to prime him, he stared uncomfortably at the light switch and offered me close to nothing (embarrassing for both of us)
  • one candidate walked up to the light switch and began testing it as she walked me through her thought process. After some solid high level tests, she wanted to see electrical schematics for the building and asked me all kinds of questions about emergency backup power, how many amps the room’s lights draw, and what else was on that circuit. She wanted to remove the trim plate to check the wiring for electrical code standards. She asked if the room’s lights could be controlled by a master switch somewhere else or an energy saver timer for off-hours. (these types of questions/tests make her a good fit for my team because my AUT’s weakest test area is its integration with other systems)
  • one candidate was good at coming up with cosmetic and usability tests (e.g., Is the switch labeled well? Can I reach it from the doorway when the room is dark? Does the trim plate match the room’s trim in color and style?)…not so important for my AUT but good tests for others perhaps.
  • one candidate went right for stress tests. He flipped the lights on/off as quickly as he could. He tried to force the switch to stay in the halfway-off-halfway-on position to see if it sparked or flickered the lights.
More was revealed about the confidence of each candidate, their creativity, how technical their brain was, how quickly their mind worked, their persistence, and finally how interested they were in determining their mission and what I thought was important to know.


  1. macbookpros said...

    I LOLed at the 3rd one. I almost felt uncomfortable reading it myself.

    The 4th one seems really inquisitive like you. And probably would be almost as annoying as well. Just kidding :)

    Also maybe regarding the 3rd one you should have a backup plan to ask them to test something else that might seem a bit less out of the ordinary -- like testing the calculator app in Windows (bonus points if they try dividing by zero).

  2. Sandeep Maher said...

    Eric, Quite a worthwhile question and something which tells you more than a thing or two about the interviewee I agree. I too pose similar questions where only the subject changes from a light switch to say a game (first person shooter), a camcorder or a hard disk and some such...maybe even a pencil... Some get asked in a written form & sometimes in face-to-face round.. I look at the written word also because it tells me something about their flow of thoughts, logic, handwriting, neatness, and so on..

    The reactions (verbal and behavioural) and the answers tells you how quickly people can think on their feet and respond to questions which come straight from the blue.. its like an interviewee entering the room and you throw something at him & say 'catch'.

  3. Joe said...

    Just curious...

    Does your company produce light switches?

    Have you found a positive correlation between "good answers" to your question and a new hire's testing ability?

    When you were hired, did you have to answer this question?

    Have you considered the possibility that candidates might dismissed your company based on the kinds of questions asked during interviews?

  4. Devon said...

    Great Post. I love QA interview questions. I'm in the process of interviewing right now, and there is such a difference in the way people approach problems they don't expect.
    This is a good question! nice post.

    I've blogged some of my favorite questions here http://ladybug010.wordpress.com/2010/01/18/qa-jobs-resumes-and-interviews/

  5. Eric Jacobson said...


    Ha! No, my company does not produce light switches.

    Those are good questions.

    No, I was certainly not asked to test a light switch during my interview. I had it very easy.

    Positive correlation? Well, we haven't hired anyone that has been asked to test the light switch, so it is too early to tell. But I can tell you, the candidate described in bullet 4 was my first choice and is coming in next week for another interview.

    And finally, if someone is turned off by my light switch question, I certainly hope they lose interest in my tester position. Because I wouldn't want them on my team. Successful testers on my team are good at thinking on their feet and coming up with good tests quickly.

  6. ElizaF said...

    I think interview approaches like this certainly do seperate the wheat from the chaff.

    A good tester will have a systematic approach to testing that they can apply to any given scenario without hesitation.

    The one I got many moons ago was to document the tests for extracting a can from a lemonade vending machine.

    I did the whole pre.req.s, examined the testing environment, verified the machine was "fit for testing" and began the "tests"
    (Put in too little money, have money refunded, put in correct money, have money refunded etc. etc) then when I did eventually press vend, the can got stuck instead of dropping to the tray.
    So I applied the "workaround" of rocking the machine with my sholder.

    My "report" concluded that the machine was periodically unfit for purpose unless a physio could also be "installed" in the building to deal with the multiple aching sholders that would result from its "implimentation".

    I got the job because out of all the interviewees for the role, I was the only one who physically tackled the machine :)

  7. amath80 said...

    It a good thing if you have some back up light switch when you test it. it just for second thought.

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