This is one of the most common interview questions for developer, tester, program manager or architect positions. The other variations may include testing light bulb, toaster, elevator, oven, dishwasher, freezer and etc. Another quite common variation is the specific ask for at least 10-15 test cases.

Slightly rephrased the two most common answer are “Uh…Um.. Ur..I dunnow… Turn it on? ” and “Hey… I am not some tester, I am DEVELOPER”

So, here I want to share what are the most interviewers are probably looking for and how to approach this question in the structured way.

So first thing first, why do they ask this question? The answer, is to check candidates systematic thinking, creativity, attention to details and the most important knowledge of testing methodologies.

Keeping this in mind below is the answer I would suggest. Remember, you need to showcase your knowledge and creativity, so if you stick to the structure approach you actually can go really bizarre with the test cases. Ideally, you should show that no single brand we see now in stores would pass your QA tests.

Sample Answer:

Well, I am not familiar enough with the electrical engineering and don’t have specifics about this Kettle implementation, so I can perform only black box testing against the spec. I also assume kettle is designed for US Market and should work from 110V electric outlet. All tests are using 110V outlet at optimal operational temperature, on normal altitude, if not specified over wise.

For the beginning, I would start with functional testing and the first set of functional test cases I indentify would also serve as BVT set.

Build Verification Tests (BVTs)

#1. Plug kettle in the wall outlet, pour the water up to minimum mark, turn the kettle on. Verify that the kettle auto turned off and the water temperature in equal or greater than 100C.

#2. Plug kettle in the wall outlet, pour the water up to maximum mark, turn the kettle on. Verify that the kettle auto turned off and the water temperature in equal or greater than 100C.

#3. Pour the minimal allowed amount of water, verify that the water level mark is displaying correct water level at the minimum mark

#5. Pour the maximum allowed amount of water, verify that the water level mark is displaying correct water level at the maximum mark

#6. Pour water up to the maximum level in the kettle, then transfer water into external measured container to verify that maximum mark indicates X gallons according to spec

#7. Plug kettle in the wall outlet, pour minimum allows amount of water into the kettle and turn it on. Verify that ON light is lighted and stays ON all time while kettle works

I would keep BVT set to no more than 10 test cases to make sure they execute fast and notify about potential build breaks ASAP.

Edge condition testing:

#1. Plug kettle in the wall outlet, don’t pour any water and turn the kettle ON. Make sure device behaves according to the spec.

#2. Plug kettle in the wall outlet, over pour water above maximum mark and turn the kettle ON. Make sure device behaves according to the spec.

#3. Use adapter to plug kettle in European 220V wall outlet, pour minimum allows amount of water into the kettle and turn ON. Make sure device behaves according to the spec. i.e safety mechanism such as fuse box was triggered, no smoke, fire, electricity.

#4. Plug kettle in the wall outlet, remove kettle from the foundation and drop base into the water container. Verify that fuse box disconnected electricity, again no fire, electric shock, etc.

#5. Plug kettle in the wall outlet, pour oil/benzene into the kettle up to the maximum mark, turn it ON. Make sure device behaves according to the spec. Ideally it should have substance detector build in and warn user about improper use.

#6. Plug kettle in the wall outlet, with the room warmed to maximum operational temperature according to spec. Pour water into the kettle up to the maximum mark and turn it ON. Verify that the water is warmed to 100C and kettle turns off automatically.

#7. Plug kettle in the wall outlet, with the room cooled to minimal operational temperature according to spec. Pour water into the kettle up to the maximum mark and turn it ON. Verify that the water is warmed to 100C and kettle turns off automatically.

#8. Plug kettle in the wall outlet, fill the kettle with the ice cubes up to the maximum mark and turn it ON. Verify that the water is warmed to 100C and kettle turns off automatically.

#9 Repeat test cases #6 and #7 but going above or below allowed temperature. Verify that the device fails safely.

Performance testing:

#1. Plug kettle in the wall outlet, pour water into the kettle up to the maximum mark, turn it ON. Repeat 100 times. verify that in average it boils the water in the time recorded in the spec

#2. Plug kettle in the wall outlet, increase atmospheric pressure in the testing room to simulate low altitudes, pour water into the kettle up to the maximum mark, turn it ON. Repeat 100 times. verify that in average it boils the water in the time recorded in the spec

#3. Plug kettle in the wall outlet, decrease atmospheric pressure in the testing room to simulate high altitudes, pour water into the kettle up to the maximum mark, turn it ON. Repeat 100 times. verify that in average it boils the water in the time recorded in the spec


The list can go on, with stress testing, load testing, usability/accessibility testing (can older person with arthritis still use it?), security testing (is the device have smart lock from kids?), and so on.

But i think I made my point. If the interviewer asks you to play this game, then simply play it along and bring to the bizarre level introducing new and new test cases and demanding features and functionality never seen before in the kettle, toaster, elevator and ect. This is exactly what they are looking for.



Company where asked this question: Amazon






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