[racket] unit test for close enough values

> check-= wants single value but unfortunately my values are wrapped in set of vectors.

Oh I didn't notice that.

In that case you could define your own check -- that looks inside the
sets and vectors to do the approximate equality test -- using the
second variant of `define-binary-check` as described here:

http://docs.racket-lang.org/rackunit/api.html#%28form._%28%28lib._rackunit%2Fmain..rkt%29._define-binary-check%29%29