ocaml-containers/qCheck.ml

(*
copyright (c) 2013, simon cruanes
all rights reserved.

redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

redistributions of source code must retain the above copyright notice, this
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*)

(** {6 Quickcheck inspired property-based testing} *)

module Arbitrary = struct
  type 'a t = Random.State.t -> 'a

  let return x st = x

  let int n st = Random.State.int st n

  let int_range ~start ~stop st =
    let n = stop - start in
    if n <= 0
      then 0
      else start + Random.State.int st n

  let (--) start stop = int_range ~start ~stop

  let small_int = int 100

  let bool = Random.State.bool

  let float f st = Random.State.float st f

  let char st = Char.chr (Random.State.int st 128)

  let alpha st =
    Char.chr (Char.code 'a' + Random.State.int st (Char.code 'z' - Char.code 'a'))

  let string_len len st =
    let n = len st in
    assert (n>=0);
    let s = String.create n in
    for i = 0 to n-1 do
      s.[i] <- alpha st
    done;
    s

  let string st = string_len (int 10) st

  let map ar f st = f (ar st)

  let rec _make_list ar st acc n =
    if n = 0 then acc else
      let x = ar st in
      _make_list ar st (x::acc) (n-1)

  let list ?(len=int 10) ar st =
    let n = len st in
    _make_list ar st [] n

  let opt ar st =
    if Random.State.bool st
      then Some (ar st)
      else None

  let list_repeat len ar st =
    _make_list ar st [] len

  let array ?(len=int 10) ar st =
    let n = len st in
    Array.init n (fun _ -> ar st)

  let array_repeat n ar st =
    Array.init n (fun _ -> ar st)

  let among_array a st =
    let i = Random.State.int st (Array.length a) in
    a.(i)

  let among l = among_array (Array.of_list l)

  let choose l =
    assert (l <> []);
    let a = Array.of_list l in
    fun st ->
      let i = Random.State.int st (Array.length a) in
      a.(i) st

  let _fix ~max ~depth recursive f =
    let rec ar = lazy (fun st -> (Lazy.force ar_rec) st)
    and ar_rec = lazy (f ar) in
    Lazy.force ar

  let fix ?(max=max_int) ~base f =
    let rec ar = lazy
      (fun depth st ->
        if depth >= max || Random.State.int st max < depth
          then base st (* base case. THe deeper, the more likely. *)
        else  (* recurse *)
          let ar' = Lazy.force ar (depth+1) in
          f ar' st)
    in
    Lazy.force ar 0

  let fix_depth ~depth ~base f st =
    let max = depth st in
    fix ~max ~base f st

  let lift f a st = f (a st)

  let lift2 f a b st = f (a st) (b st)

  let lift3 f a b c st = f (a st) (b st) (c st)

  let lift4 f a b c d st = f (a st) (b st) (c st) (d st)

  let pair a b = lift2 (fun x y -> x,y) a b

  let triple a b c = lift3 (fun x y z -> x,y,z) a b c

  let quad a b c d = lift4 (fun x y z w -> x,y,z,w) a b c d

  let (>>=) a f st =
    let x = a st in
    f x st

  let generate ?(n=100) ?(rand=Random.State.make_self_init()) gen =
    let l = ref [] in
    for i = 0 to n-1 do
      l := (gen rand) :: !l
    done;
    !l
end

(** {2 Pretty printing} *)

module PP = struct
  type 'a t = 'a -> string

  let int = string_of_int
  let bool = string_of_bool
  let float = string_of_float
  let string s = s
  let char c =
    let s = "_" in
    s.[0] <- c;
    s

  let pair a b (x,y) = Printf.sprintf "(%s, %s)" (a x) (b y)
  let triple a b c (x,y,z) = Printf.sprintf "(%s, %s, %s)" (a x) (b y) (c z)
  let quad a b c d (x,y,z,w) =
    Printf.sprintf "(%s, %s, %s, %s)" (a x) (b y) (c z) (d w)

  let list pp l =
    let b = Buffer.create 25 in
    Buffer.add_char b '(';
    List.iteri (fun i x ->
      if i > 0 then Buffer.add_string b ", ";
      Buffer.add_string b (pp x))
      l;
    Buffer.add_char b ')';
    Buffer.contents b

  let array pp a = 
    let b = Buffer.create 25 in
    Buffer.add_char b '[';
    Array.iteri (fun i x ->
      if i > 0 then Buffer.add_string b ", ";
      Buffer.add_string b (pp x))
      a;
    Buffer.add_char b ']';
    Buffer.contents b
end

(** {2 Testing} *)

module Prop = struct
  type 'a t = 'a -> bool

  exception PrecondFail
  
  let assume p =
    if not p then raise PrecondFail

  let assume_lazy (lazy p) =
    if not p then raise PrecondFail

  let (==>) a b =
    fun x ->
      assume (a x);
      b x

  let (&&&) a b x = a x && b x

  let (|||) a b x = a x || b x

  let (!!!) a x = not (a x)
end

type 'a result =
  | Ok of int * int  (* total number / precond failed *)
  | Failed of 'a list
  | Error of exn

(* random seed, for repeatability of tests *)
let __seed = [| 89809344; 994326685; 290180182 |]

let check ?(rand=Random.State.make __seed) ?(n=100) gen prop =
  let precond_failed = ref 0 in
  let failures = ref [] in
  try
    for i = 0 to n - 1 do
      let x = gen rand in
      try
        if not (prop x)
          then failures := x :: !failures
      with Prop.PrecondFail ->
        incr precond_failed
    done;
    match !failures with
    | [] -> Ok (n, !precond_failed)
    | _ -> Failed (!failures)
  with e ->
    Error e

(** {2 Main} *)

type 'a test_cell = {
  n : int;
  pp : 'a PP.t option;
  prop : 'a Prop.t;
  gen : 'a Arbitrary.t;
  name : string;
}
type test =
  | Test : 'a test_cell -> test
  (** GADT needed for the existential type *)

let mk_test ?(n=100) ?pp ?(name="<anon prop>") gen prop =
  Test { prop; gen; name; n; pp; }

let run ?(out=stdout) ?(rand=Random.State.make __seed) (Test test) =
  Printf.fprintf out "testing property %s...\n" test.name;
  match check ~rand ~n:test.n test.gen test.prop with
  | Ok (n, prefail) ->
    Printf.fprintf out "  [✔] passed %d tests (%d preconditions failed)\n" n prefail;
    true
  | Failed l ->
    begin match test.pp with
    | None -> Printf.fprintf out "  [×] %d failures\n" (List.length l)
    | Some pp ->
      Printf.fprintf out "  [×] %d failures:\n" (List.length l);
      List.iter
        (fun x -> Printf.fprintf out "  %s\n" (pp x))
        l
    end;
    false
  | Error e ->
    Printf.fprintf out "  [×] error: %s\n" (Printexc.to_string e);
    false

type suite = test list

let flatten = List.flatten

let run_tests ?(out=stdout) ?(rand=Random.State.make __seed) l =
  let start = Unix.gettimeofday () in
  let failed = ref 0 in
  Printf.fprintf out "check %d properties...\n" (List.length l);
  List.iter (fun test -> if not (run ~out ~rand test) then incr failed) l;
  Printf.fprintf out "tests run in %.2fs\n" (Unix.gettimeofday() -. start);
  if !failed = 0
    then Printf.fprintf out "[✔] Success!\n"
    else Printf.fprintf out "[×] Failure (%d tests failed).\n" !failed;
  !failed = 0