diff --git a/src/testlib/containers_testlib.ml b/src/testlib/containers_testlib.ml
new file mode 100644
index 00000000..97a16c3e
--- /dev/null
+++ b/src/testlib/containers_testlib.ml
@@ -0,0 +1,175 @@
+
+module Q = QCheck
+let spf = Printf.sprintf
+
+type 'a eq = 'a -> 'a -> bool
+type 'a print = 'a -> string
+
+module Test = struct
+
+  type run =
+    | T of (unit -> bool)
+    | Eq : {
+      eq: 'a eq option;
+      print: 'a print option;
+      lhs: 'a;
+      rhs: 'a;
+    } -> run
+    | Q : {
+      count: int option;
+      arb: 'a Q.arbitrary;
+      prop: 'a -> bool;
+    } -> run
+
+  type t = {
+    __FILE__: string;
+    __LINE__: int;
+    run: run;
+  }
+
+  (** Location for this test *)
+  let str_loc (self:t) : string =
+    Printf.sprintf "(test :file '%s' :line %d)" self.__FILE__ self.__LINE__
+
+  let mk ~__FILE__ ~__LINE__ run : t =
+    { __FILE__; __LINE__; run }
+
+  let run ~seed (self:t) : _ result =
+    match
+      match self.run with
+      | T f ->
+        if f() then Ok() else Error "failed: returns false"
+      | Eq {eq; print; lhs; rhs} ->
+        let eq = match eq with Some f->f | None -> (=) in
+        if eq lhs rhs then Ok ()
+        else (
+          let msg = match print with
+            | None -> "failed: not equal"
+            | Some p -> spf "failed: not equal:\nlhs=%s\nrhs=%s" (p lhs) (p rhs)
+          in
+          Error msg
+        )
+      | Q {count; arb; prop} ->
+
+        (* create a random state from the seed *)
+        let rand =
+          let bits = String.to_seq seed |> Seq.map Char.code |> CCArray.of_seq in
+          Random.State.make bits
+        in
+
+        let module Fmt = CCFormat in
+        let cell = Q.Test.make_cell ?count ~name:(str_loc self) arb prop in
+
+        let pp_cex out (cx: _ Q.TestResult.counter_ex) =
+          let {Q.TestResult.instance; shrink_steps=n; msg_l} = cx in
+          let msg_l = if msg_l =[] then "" else "\n" ^ String.concat "\n" msg_l in
+          match arb.print with
+          | None -> Fmt.fprintf out "<instance> (after %d shrink steps)%s" n msg_l
+          | Some p ->
+            Fmt.fprintf out "`%s` (after %d shrink steps)%s" (p instance) n msg_l
+        in
+
+        (* TODO: if verbose, print stats, etc. *)
+
+        let res = Q.Test.check_cell ~rand cell in
+
+        begin match Q.TestResult.get_state res with
+        | QCheck2.TestResult.Success -> Ok ()
+        | QCheck2.TestResult.Failed { instances } ->
+          let msg = Format.asprintf "@[<v2>failed on instances:@ %a@]"
+            (Fmt.list ~sep:(Fmt.return ";@ ") pp_cex) instances
+          in
+          Error msg
+        | QCheck2.TestResult.Failed_other {msg} ->
+          let msg = spf "failed: %s" msg in
+          Error msg
+        | QCheck2.TestResult.Error {instance; exn; backtrace} ->
+          let msg = Format.asprintf "@[<v2>raised %s@ on instance %a@ :backtrace %s@]"
+            (Printexc.to_string exn) pp_cex instance backtrace
+          in
+          Error msg
+        end
+    with
+    | res -> res
+    | exception e ->
+        Error (spf "failed: raised %s" (Printexc.to_string e))
+        end
+
+let all_ : Test.t list ref = ref []
+let add_ t = all_ := t :: !all_
+
+module Prelude = struct
+  module Q = QCheck
+
+  let t ~__FILE__ ~__LINE__ f : unit =
+    add_ @@ Test.mk ~__FILE__ ~__LINE__ @@ Test.T f
+
+  let eq ~__FILE__ ~__LINE__ ?cmp ?printer lhs rhs : unit =
+    add_ @@ Test.mk ~__FILE__ ~__LINE__ @@ Test.Eq {eq=cmp; print=printer; lhs; rhs}
+
+  let q ~__FILE__ ~__LINE__ ?count arb prop : unit =
+    add_ @@ Test.mk ~__FILE__ ~__LINE__ @@ Test.Q {arb; prop; count}
+
+  let assert_equal ?printer ?(cmp=(=)) x y : unit =
+    if not @@ cmp x y then (
+      match printer with
+      | None -> failwith "not equal"
+      | Some p ->
+        failwith @@ spf "not equal: lhs=%s, rhs=%s" (p x) (p y)
+    )
+end
+
+let run_all ?seed:seed_hex ~descr () : unit =
+  let start = Unix.gettimeofday() in
+
+  (* generate or parse seed *)
+
+  let seed_hex = match seed_hex, Sys.getenv_opt "SEED" with
+    | Some s, _ -> s
+    | None, Some s -> s
+    | None, None ->
+      Random.self_init();
+      let a = CCList.init 8 (fun _ -> Random.int 256 |> Char.chr) in
+      CCString.to_hex @@ CCString.of_list a
+  in
+
+  let seed = match CCString.of_hex seed_hex with
+    | Some s->s
+    | None ->
+      Format.printf "error: seed must be a hex string: %S@." seed_hex; exit 1
+  in
+
+  Format.printf "seed: %s@." seed_hex;
+
+  (* now run the suite *)
+
+  let suite = List.rev !all_ in
+  Format.printf "testing %s: running %d tests…@." descr (List.length suite);
+  let failed = ref [] in
+
+  List.iter (fun t ->
+    (*
+      NOTE: we probably want this to be silent?
+      Format.printf "> run %s@." (Test.str_loc t);
+      *)
+    match Test.run ~seed t with
+    | Ok () -> ()
+    | Error msg ->
+      Format.printf "FAILED: %s@." (Test.str_loc t);
+      failed := (Test.str_loc t, msg ) :: !failed;
+  ) suite;
+
+  Format.printf "%d tests done in %.3fs@." (List.length suite)
+    (Unix.gettimeofday() -. start);
+
+  match !failed with
+  | [] ->
+    Format.printf "OK@."
+  | _f ->
+    Format.printf "ERROR (%d failures)@." (List.length _f);
+    List.iter (fun (w,msg) ->
+      Format.printf "@.========@.failed %s:@.%s@." w msg)
+    _f;
+    exit 1
+
+
diff --git a/src/testlib/containers_testlib.mli b/src/testlib/containers_testlib.mli
new file mode 100644
index 00000000..ed6b471e
--- /dev/null
+++ b/src/testlib/containers_testlib.mli
@@ -0,0 +1,17 @@
+
+type 'a eq = 'a -> 'a -> bool
+type 'a print = 'a -> string
+
+
+module Prelude : sig
+
+  module Q = QCheck
+
+  val t : __FILE__:string -> __LINE__:int -> (unit -> bool) -> unit
+  val eq : __FILE__:string -> __LINE__:int -> ?cmp:'a eq -> ?printer:'a print -> 'a -> 'a -> unit
+  val q : __FILE__:string -> __LINE__:int -> ?count:int -> 'a Q.arbitrary -> ('a -> bool) -> unit
+
+  val assert_equal : ?printer:'a print -> ?cmp:'a eq -> 'a -> 'a -> unit
+end
+
+val run_all : ?seed:string -> descr:string -> unit -> unit
diff --git a/src/testlib/dune b/src/testlib/dune
new file mode 100644
index 00000000..e07a46ae
--- /dev/null
+++ b/src/testlib/dune
@@ -0,0 +1,5 @@
+
+(library
+  (name containers_testlib)
+  (synopsis "Test library for containers")
+  (libraries containers qcheck-core unix))