diff --git a/src/Tiny_httpd_util.ml b/src/Tiny_httpd_util.ml
index b5009de0..f2b769e2 100644
--- a/src/Tiny_httpd_util.ml
+++ b/src/Tiny_httpd_util.ml
@@ -1,3 +1,14 @@
+
+(* test utils *)
+(*$inject
+  let pp_res f = function Ok x -> f x | Error e -> Printexc.to_string e
+  let pp_res_query = (Q.Print.(pp_res (list (pair string string))))
+  let err_map f = function Ok x-> Ok (f x) | Error e -> Error e
+  let sort_l l = List.sort compare l
+  let eq_sorted a b = (=) (err_map sort_l a)(err_map sort_l b)
+  let is_ascii_char c = Char.code c < 128
+*)
+
 let percent_encode ?(skip=fun _->false) s =
   let buf = Buffer.create (String.length s) in
   String.iter
@@ -11,6 +22,12 @@ let percent_encode ?(skip=fun _->false) s =
     s;
   Buffer.contents buf
 
+(*$= & ~printer:(fun s->s)
+  "hello%20world" (percent_encode "hello world")
+  "%23%25^%24%40^%40" (percent_encode "#%^$@^@")
+  "a%20ohm%2b5235%25%26%40%23%20---%20_" (percent_encode "a ohm+5235%&@# --- _")
+*)
+
 let hex_int (s:string) : int = Scanf.sscanf s "%x" (fun x->x)
 
 let percent_decode (s:string) : _ option =
@@ -35,6 +52,13 @@ let percent_decode (s:string) : _ option =
     Some (Buffer.contents buf)
   with Exit -> None
 
+(*$QR & ~count:1_000 ~long_factor:20
+    Q.string (fun s ->
+        String.iter (fun c -> Q.assume @@ is_ascii_char c) s;
+        match percent_decode (percent_encode s) with
+        | Some s' -> s=s'
+        | None -> Q.Test.fail_report "invalid percent encoding")
+*)
 
 let parse_query s : (_ list, _) result=
   let pairs = ref [] in
@@ -63,3 +87,19 @@ let parse_query s : (_ list, _) result=
     Ok !pairs
   with e -> Error e
 
+(*$= & ~printer:pp_res_query ~cmp:eq_sorted
+  (Ok ["a", "b"; "c", "d"]) (parse_query "a=b&c=d")
+*)
+
+(*$QR & ~long_factor:20 ~count:1_000
+    Q.(small_list (pair string string))
+      (fun l ->
+        List.iter (fun (a,b) ->
+            Q.assume (a<>"" && b<>"" );
+            String.iter (fun c -> Q.assume @@ is_ascii_char c) a;
+            String.iter (fun c -> Q.assume @@ is_ascii_char c) b;
+          ) l;
+        let s = String.concat "&"
+            (List.map (fun (x,y) -> percent_encode x ^"="^percent_encode y) l) in
+        eq_sorted (Ok l) (parse_query s))
+*)
diff --git a/src/dune b/src/dune
index 202dbcb0..1ee3eba7 100644
--- a/src/dune
+++ b/src/dune
@@ -3,5 +3,6 @@
   (name tiny_httpd)
   (public_name tiny_httpd)
   (libraries threads)
+  (inline_tests (backend qtest.lib))
   (flags :standard -safe-string)
   (wrapped false))
diff --git a/tiny_httpd.opam b/tiny_httpd.opam
index 88d178a5..f76c5e23 100644
--- a/tiny_httpd.opam
+++ b/tiny_httpd.opam
@@ -14,6 +14,8 @@ depends: [
   "base-threads"
   "ocaml" { >= "4.03.0" }
   "odoc" {with-doc}
+  "qtest" {with-test}
+  "qcheck" {with-test}
 ]
 tags: [ "http" "thread" "server" "tiny_httpd" "http_of_dir" "simplehttpserver" ]
 homepage: "https://github.com/c-cube/tiny_httpd/"