fixed a contract bug

main.rkt

@@ -3,7 +3,7 @@
          racket/contract)
 (provide
  (contract-out
-  [test-files! (->* () () #:rest path-string? any/c)]
+  [test-files! (->* () () #:rest (listof path-string?) any/c)]
   [clear-coverage! (-> any)]
   [get-test-coverage (-> coverage/c)]
   [make-covered?

tests/main.rkt

@@ -3,7 +3,8 @@
 ;; for every .rkt file in those directories it loads
 ;; tests that file and checks its coverage against an
 ;; .rktl file of the same name
-(require "../cover.rkt" racket/runtime-path rackunit)
+(require (only-in "../main.rkt" test-files! clear-coverage! get-test-coverage)
+         racket/runtime-path rackunit)
 
 (define (test-dir d)
   (define files