Check predictability of names in robot-name exercise
#2110
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The README to the exercise states > The names must be random: they should not follow a predictable sequence. Yet there are accepted [solutions](https://exercism.org/tracks/rust/exercises/robot-name/solutions/boso) that violate the requirement. *) The linked solution can unfortunately not be commented on: > Comments have been disabled This new test makes sure that the most obvious kind of predictability - and probably the only one naturally used by anyone - makes tests fail. The test cannot be run concurrently with other tests, for obvious reasons, hence the not very elegant solution using a global RwLock, which every other tests has to `read()`, in order for the new test to run exclusively.
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| // just checking the easiest kind of predictable sequences here: the difference between | ||
| // numerical representation of consecutive names is always the same | ||
| let d = nums[1] - nums[0]; |
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You could easily beat that by using alternating patterns. How about compiling a set of the differences and check that its length is at least the square root of the length of the names list?
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If you really wanted to prevent any possible predictable sequence, you could get very scientific about this, and it would be impossible to achieve anyway. In the end, even PRNGs are pretty predictable. Tiny algorithms describe PRNG sequences. So where to draw the line?
The goal of this PR is to simply prevent predictable sequences that people would - and in fact did - actually use. More complicated predictable sequences make solutions less simple, so the ranking will take care of hiding them...
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The README to the exercise states
Yet there are accepted solutions that violate the requirement.
*) The linked solution can unfortunately not be commented on:
This new test makes sure that the most obvious kind of predictability - and probably the only one used naturally by anyone: enumerating names in order, rather than creating random ones - makes tests fail.
The test cannot be run concurrently with other tests, for obvious reasons, hence the not very elegant solution using a global
RwLock, which every other tests has toread(), in order for the new test to be able to run exclusively.