Add rackunit sugar for testing many different calls to a procedure

[jackfirth]

Many test cases are just a series of calls to a procedure that check what values are returned, or check that a certain exception is raised, or check that a contract or arity violation occurred. Something like this might make that more pleasant:

(test-case/procedure foo
  [(1 2 3) 'some-return-value]
  [(#:kw 1) 'some-other-return-value]
  [(1 2 3 4 5) #:raise #rx"something went wrong"]
  [(1 2 'not-a-number) #:contract-exn 'not-a-number #:expected number?]
  [() #:raise exn:fail:contract:arity]) ;; as a convenience, struct identifiers become predicate tests

Expressed without expectations, the above would be:

(test-case "foo"
  (check-equal? (foo 1 2 3) 'some-return-value)
  (check-equal? (foo #;kw 1) 'some-other-return-value)
  (check-exn #rx"something went wrong" (thunk (f 1 2 3 4 5)))
  ;; we need two checks for the contract exception to assert the expected part with a regexp
  (let ([call (thunk (f 1 2 'not-a-number))])
    (check-exn exn:fail:contract? call)
    (check-exn #rx"expeced: number?" call))
  (check-exn exn:fail:contract:arity? f))

However, the expectation tests can use expect-call to get much better error messages that include what the argument expressions evaluated to, and expectations allow much more complex assertions than just equal?, predicate, or regular expression assertions. A generic #:call keyword could act as a hook for using more general expectations that operate on the thunk representing the call.