Add contract for run-tests.

collects/rackunit/text-ui.rkt

@@ -30,6 +30,7 @@
 
 (require racket/match
          racket/pretty
+         racket/contract
          "private/base.rkt"
          "private/counter.rkt"
          "private/format.rkt"
@@ -39,10 +40,15 @@
          "private/monad.rkt"
          "private/hash-monad.rkt"
          "private/name-collector.rkt"
-         "private/text-ui-util.rkt")
+         "private/text-ui-util.rkt"
+         "private/test.rkt")
 
-(provide run-tests
-         display-context
+(provide/contract 
+ [run-tests (((or/c test-case? test-suite?)) 
+             ((or/c 'quiet 'normal 'verbose))
+             . ->* . exact-nonnegative-integer?)])
+
+(provide display-context
          display-exn
          display-summary+return
          display-ticker