[racket] Tests before of to define the function

In Beginning Student mode I can to define a test before of the function:

(check-expect (double 2) 4)
(define (double n)
     (* n 2))

In #lang racket, the next code fails:

(require rackunit)
(check-equal? (double 2) 4)
(define (double n)
     (* n 2))

Is it possible to write the tests before of the functions in racket, 
like in BS?