diff --git a/main.rkt b/main.rkt
index 66595fd..8e41e71 100644
--- a/main.rkt
+++ b/main.rkt
@@ -13,15 +13,17 @@
 
 (define (test-files . paths)
   (for ([p paths])
-    (define stx 
-      (with-module-reading-parameterization (thunk (read-syntax p (open-input-file p)))))
-    (define-values (name anned) 
+    (define stx
+      (with-module-reading-parameterization
+          (thunk (read-syntax p (open-input-file p)))))
+    (define-values (name anned)
       (syntax-parse (expand stx)
         #:datum-literals (module)
         [(~and s (module name:id lang forms ...))
          (values (syntax-e #'name)
                  (annotate-top #'s (namespace-base-phase ns)))]))
     (eval-syntax anned ns)
+    ;; TODO run test/given submodule
     (parameterize ([current-namespace ns])
       (namespace-require `',name)))
   coverage)
@@ -30,3 +32,44 @@
   (dict-clear! coverage)
   (set! ns (make-base-empty-namespace))
   (namespace-attach-module (current-namespace) "coverage.rkt" ns))
+
+(define (test-coverage-annotations)
+  ;; can-annotate : (listof (list boolean srcloc))
+  ;; boolean is #t => code was run
+  ;;            #f => code was not run
+  ;; remove those that cannot be annotated
+  (define can-annotate
+    (filter values
+            (for/list ([(stx covered?) coverage])
+              (and (syntax? stx)
+                   (let ([src (syntax-source stx)]
+                         [pos (syntax-position stx)]
+                         [span (syntax-span stx)])
+                     (and pos
+                          span
+                          #;
+                          (hash-ref! port-name-cache src
+                                     (λ () (send (get-defs) port-name-matches? src)))
+                          (list covered?
+                                (make-srcloc src #f #f pos span))))))))
+
+  ;; filtered : (listof (list boolean srcloc))
+  ;; remove redundant expressions
+  (define filtered
+    ;; actions-ht : (list src number number) -> (list boolean syntax)
+    (let ([actions-ht (make-hash)])
+      (for-each
+       (λ (pr)
+         (let* ([on? (list-ref pr 0)]
+                [key (list-ref pr 1)]
+                [old (hash-ref actions-ht key 'nothing)])
+           (cond
+            [(eq? old 'nothing) (hash-set! actions-ht key on?)]
+            [old ;; recorded as executed
+             (void)]
+            [(not old) ;; recorded as unexected
+             (when on?
+               (hash-set! actions-ht key #t))])))
+       can-annotate)
+      (hash-map actions-ht (λ (k v) (list v k)))))
+  filtered)
diff --git a/tests/basic/prog.rkt b/tests/basic/prog.rkt
new file mode 100644
index 0000000..4b8e994
--- /dev/null
+++ b/tests/basic/prog.rkt
@@ -0,0 +1,2 @@
+#lang racket
+(+ 1 2)