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by vbezhenar 4077 days ago
The great value of unit testing is reproducibility. You can't always find the cause of the bug just from failed test logs. You might need to re-run the test to debug and tweak the code. And if your test is randomly failing, it would be quite tricky to do that.

Randomness is OK. Just make sure that RNG yields the same values each time test run. For example in Java the class Random is guaranteed to yield the same values for the same seed. I'm not sure that JavaScript has this class, probably you'll have to write your own version or find it in some library.
2 comments
collyw 4077 days ago
I would argue the opposite. Running a passing test over and over again when a piece of code hasn't changed doesn't actually gain you anything (though if you are refactoring it will). Using randomness will test a lot more cases.
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egeozcan 4077 days ago
You can generate random test cases (and save them), given that you have no performance worries. However, introducing randomness inside a test doesn't make so much sense, as one of the grandparents states, because the point of testing is predictability. When a test which does things differently every time it runs fails once, it is not totally useless information but much less informative than a test which always fails.

I should also mention that there are a lot of cases where randomness wouldn't affect the result[1], but then, why introduce randomness in the first place?

If the aim is to test as many combinations of different variables as possible, bunch of tight, nested loops would be much reliable IMHO.

[1] for example, if a list doesn't render correctly with n elements, it is very likely that it still wouldn't with m elements - unless you have performance problems and that means you need to test for the maximum sane values and limit the input

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matthewmacleod 4077 days ago
You're right, but I would at least class that as a different sort of testing – it's much closer to e.g. fuzzing than unit testing. Both are valuable though.
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vkjv 4077 days ago
My thoughts exactly. Randomness has a place in tests, but not in unit tests.
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TheAceOfHearts 4077 days ago
Chance.js[0] is a great JS lib that lets you do precisely that for a wide array of values.

[0]: http://chancejs.com/

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modnine 4077 days ago
Thank you for this. This lib looks very promising.
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