Some shrinkers are incomplete

[Gbury]

Some shrinkers only try a few possibles values: for instance the default shrinker for integers try to divide the integer by 2, but if that fails, it doesn't try further. One example of problematic behavior is the following:

let test =
  QCheck.Test.make ~count:1000 ~name:"mod3"
   QCheck.int (fun i -> i mod 3 <> 0);;

which results in:

QCheck_runner.run_tests [test];;
random seed: 275954313
--- Failure --------------------------------------------------------------------
Test mod3 failed (0 shrink steps):

-4393318161250674747
================================================================================
failure (1 tests failed, 0 tests errored, ran 1 tests)

giving a very non-minimal counter-example, instead of the obvious 0, because shrinking failed at the first step.

I think shrinkers should always cover the totality of smaller values, using a 'smart' ordering, much like what is done in the case of lists and arrays (where all sub-lists are tried). So I think the integer shrinker (and possibly others) should probably be fixed, unless there is a compelling argument not to do it ?

[c-cube]

Quite reasonable indeed.