relocate test in submodule

tests/test-langs.rkt

@@ -35,8 +35,9 @@
 (define (run file)
   (with-output-to-string (λ() (system (format "racket ~a" file)))))
 
-(check-equal? (run "test.ptree") "'(pagetree-root test ====)")
-(check-equal? (run "test.html.pm") "'(root \"test\" \"\\n\" \"====\")")
-(check-equal? (run "test.html.pmd") "'(root (h1 ((id \"test\")) \"test\"))")
-(check-equal? (run "test.html.pp") "test\n====")
-(check-equal? (run "test.no-ext") "test\n====")
+(module+ main
+  (check-equal? (run "test.ptree") "'(pagetree-root test ====)")
+  (check-equal? (run "test.html.pm") "'(root \"test\" \"\\n\" \"====\")")
+  (check-equal? (run "test.html.pmd") "'(root (h1 ((id \"test\")) \"test\"))")
+  (check-equal? (run "test.html.pp") "test\n====")
+  (check-equal? (run "test.no-ext") "test\n===="))