# “How do you test a vacuum?” Interview question

I have a question regarding an interview question that was asked to me recently. How are you suppose to answer if someone ask you “How do you test a vacuum”? Seems like too vague like there is so many ways to test a vacuum. How does the interview expect me to answer this question? Like what type of test methodologies I will use to test it?

• Did they mean an absence of air or did they mean a device used for cleaning? – JAB Apr 20 '18 at 2:18
• @JAB or did they mean Swedish music band popular in nineties – Alexey R. Apr 20 '18 at 11:15
• I would probably ask how they test if their cat is pregnant and leave. A business negotiation is not the place for non-work related questions. If they are entitled to stupid questions, so am I. – Rui F Ribeiro Apr 20 '18 at 11:16
• @RuiFRibeiro What. – maxathousand Apr 20 '18 at 13:25
• Hint: if the interviewer is smart then the question is designed to elicit a signal about how you handle a vague, under-specified situation. Vague, under-specified scenarios are common in industry. – Eric Lippert Apr 20 '18 at 16:49

Such open-ended questions are trying to uncover if you have real-life experience tracking down misunderstanding and unsaid assumptions (which are always the source of the biggest problems in QA), if you have experience of quickly learning about new problem area.

They are not concerned about right and wrong answers. If interviewer has a preconceived "right" answer: run!

• How is vacuum defined (empty space vs appliance vs outer space vs vacuum tube vs ...)?
• What are unsaid assumptions? What else I need to know?
• What are the requirements for vacuum?
• What are the goals/intended use? Who is the audience: users? production line?
• What process needs to be tested? Are they defined, or they need to be established and/or adjusted?
• What metrics we use to evaluate success/progress?
• What are corner/edge cases of definition? Lifecycle? Special unusual use cases?

Then, adjust answer accordingly to what you just learned. Use some related previous experience to illustrate how you solved any similar problem in the past.

They do not expect you to solve on the spot the technical problems they have and spend months and years trying to solve. They are interested to find out how you think, learn, solve problems and communicate with peers, especially under a pressure.

• "under pressure", hmm? – aschepler Apr 20 '18 at 22:48

Whenever I get the "how do you test x' questions I fall back to the tried and true:

• How should it initially appear - smoke test
• How should it work - happy path
• How should it fail - sad paths. This is usually most of the response to the interview question
• How should optional components work correctly - happy optional path
• How should optional components fail - sad optional paths

I also think about what I should do in terms of the traditional agile testing quadrants, at least those that apply and so I would consider things like:

• Unit tests - Does the vacuum suck correctly ? Does each wheel work well ?
• Integrated tests - Do the power plant, suction model and collection bag work together ?
• User Acceptance - Does it clean sufficiently ? Is the handle suitable for pushing and pulling ?
• Performance - Is the noise level acceptable? Does it get too hot ? Is the power cable safe ?

Next I would look at the test pyramid to help guide me about how many I should be writing in each area

                       manual tests
a few automated UI tests
quite a few integrated tests
lots and lots of very fast unit tests

• Missing the most important questions regarding what the desired outcomes or behaviors are. Also assumes properties and functionalities. – Alan Larimer Apr 20 '18 at 12:56
• Desired outcome: how it should initially appear. Desired outcome: how it should work on the happy path, etc. Not sure I get that point. Assuming functionality: maybe but happy and sad tests test functionality so I don't really get your point @AlanLarimer – Michael Durrant Apr 20 '18 at 15:20

There is a joke

A code tester walks into a bar. Orders a beer. Orders ten beers. Orders 2.15 billion beers. Orders -1 beers. Orders a nothing. Orders a cat. Tries to leave without paying.

Basically, tester's main job is to break things. It is job of coming up with edge cases that no one came up with before. Anyone can tell you how to test a vacuum's happy-path. Just put some dirt on a carpet and vacuum it up.

So this question is all about figuring out if you can come up with "weird" edge cases, that people normally don't think of.

• What happens when plug is pulled when it is running?
• What happens when it is dropped from first floor while running?
• What happens when you suck up bucket of water?

It is exercise in brainstorming all kinds of crazy things that people can do with their vacuum.

• This is a good answer - although I disagree with your definition of what a tester's main job is. How do you know that OP means a vacuum cleaner and not a vacuum of space? I'm not confident that you can know for sure, until it's specified.... and that's what we do. We test to gain confidence in the product under test (requirements included!). So your first question would be "What type of vacuum do you mean?" – trashpanda Apr 20 '18 at 10:22
• A tester's main job is not to break things; breaking things is a means to an end. A tester's job is not to come up with crazy cases, except insofar as those inform mainstream cases. The main job of quality assurance is being an advocate for the user by ensuring that the product meets the users needs and does not harm the user. Testing should always be done with the user in mind; testing that does not inform us about possible user experiences is opportunity cost that detracts from more important work. – Eric Lippert Apr 20 '18 at 16:52
• Tester didn't order a fractional beer - not a pro tester after all. – TCSGrad Apr 20 '18 at 21:37
• Tester gets the police called on him. – Joshua Apr 20 '18 at 23:13
• Orders a . Orders a H2O. Orders a H2O2. Orders a beer, then give me all the money from the cash register. Orders the cash register. Orders an empty glass. Orders a ";DROP TABLE Beers;--... – user253751 Apr 21 '18 at 3:42

For any engineering problem, there are classroom answers and real world answers. We need to know enough to provide a solution. What failure meay mean is important, as hysterisis may impact your solution.

(You) "Describe the application"

Yesyou are entitled to ask for more informstion. But start by getting them to tell their "story". This may be part of the game. Do not insult them by not playing along. There are options that depend upon requirements, constraints, budget.

Manometer probably a keyword, not naming this might fail you. Strain guage Reiief valve Diaphragm switch Spring tube gauge Electron beam

You should also ask along the way.....

• What is the desired state and purpose (life support ? Spacecraft ?)
• What is my budget?
• Are mutiple redundant tests required?
• How accurate does the test need to be? Tolerances, pass/fail.
• How am I constrained ? A swimming pool full of Hg is OK then ?
• Is reporting required ? Of an academic standard ?

So a pattern of requirement determination is in place. I'm seious about the keywords, your education level may be on trial.

• This is similar to @Euphoric's answer - you've assumed they're talking about the vacuum of space, where it might be a vacuum cleaner. Also, remember that this is an interview - it's okay to ask questions (and probably expected) to help form your response but, at some point, you need to start giving answers... and I can't really see an answer to OP's question here. – trashpanda Apr 20 '18 at 10:33
• I'll pay that partly. It's important to understand they may be working to a script, and you want to understand their "needs". No answer has yet mentioned standards for instance (as in BS/AS/ISO/DS) It is a pretty big jump from Vacuum to Vacuum cleaner/pump/chamber apart from grammatical construct. (test a rather than test for a). But "20 questions" is more likely to identify the application as balancing carburettors rather than NBC suit permeability. – mckenzm Apr 21 '18 at 1:09
• I very much doubt the purpose of this question is to test the candidate for specific domain knowledge. – aschepler Apr 21 '18 at 2:45