Module `Core.Only_in_test`Source

This module can be used to safely expose functions and values in signatures that should only be used in unit tests.

Under the hood, 'a t = 'a Lazy.t and the only thing that ever forces them is the force function below which should only be called in unit tests.

For example, suppose in some module, type t is actually an int. You want to keep the type definition opaque, but use the underlying representation in unit tests. You could write in the ml:

  let test_to_int t = Only_in_test.return t
  let test_of_int n = Only_in_test.return n

You would then expose in the mli:

  type t

  val test_to_int : t -> int Only_in_test.t
  val test_of_int : int -> t Only_in_test.t

Finally, if you have specific values that you might want to use in unit tests, but that have top-level side-effects or take too long to compute, you can delay the side-effects or computation until the unit tests are run by writing, e.g.:

let (test_special_value : t Only_in_test.t) = Only_in_test.of_thunk (fun () -> factorial 100)

instead of

let (test_special_value : t Only_in_test.t) = Only_in_test.return (factorial 100)

type +'a t

include Base.Monad.S with type 'a t := 'a Core.Only_in_test.t

val return : 'a 'i 'p 'q. 'a -> 'a Core.Only_in_test.t

Convert a value to a t.

val map : 
  'a 'b 'i 'j 'p 'q. 'a Core.Only_in_test.t ->
  f:('a -> 'b) ->
  'b Core.Only_in_test.t

Transforms the contents of a t.

val bind : 
  'a 'b 'i 'j 'k 'p 'q. 'a Core.Only_in_test.t ->
  f:('a -> 'b Core.Only_in_test.t) ->
  'b Core.Only_in_test.t

Sequences computations. bind t ~f computes f v for value(s) v in t. Well-behaved monads satisfy these "laws" (where ( >>= ) is the infix bind operator):

map t ~f is equivalent to bind t ~f:(fun x -> return (f x))
return x >>= f is equivalent to f x
t >>= return is equivalent to t
(t >>= f) >>= g is equivalent to t >>= fun x -> f x >>= g

val join : 
  'a 'i 'j 'k 'p 'q. 'a Core.Only_in_test.t Core.Only_in_test.t ->
  'a Core.Only_in_test.t

Combines nested t into just one layer. Equivalent to bind t ~f:Fn.id.

val ignore_m : 
  'a 'i 'j 'p 'q. 'a Core.Only_in_test.t ->
  unit Core.Only_in_test.t

Ignores contained values of t. Equivalent to map t ~f:ignore.

val all : 
  'a 'i 'p 'q. 'a Core.Only_in_test.t list ->
  'a list Core.Only_in_test.t

Combines a list of t.

val all_unit : 
  'i 'p 'q. unit Core.Only_in_test.t list ->
  unit Core.Only_in_test.t

Combines a list of t whose contents are unimportant.

val (>>=) : 
  'a 'b 'i 'j 'k 'p 'q. 'a Core.Only_in_test.t ->
  ('a -> 'b Core.Only_in_test.t) ->
  'b Core.Only_in_test.t

Infix bind.

val (>>|) : 
  'a 'b 'i 'j 'p 'q. 'a Core.Only_in_test.t ->
  ('a -> 'b) ->
  'b Core.Only_in_test.t

Infix map.

Sourcemodule Monad_infix : sig ... end

Sourcemodule Let_syntax : sig ... end

Sourceval of_thunk : (Base.Unit.t -> 'a) -> 'a Core.Only_in_test.t @@ portable

val force : 'a Core.Only_in_test.t -> 'a @@ portable

Module Core.Only_in_testSource

Module `Core.Only_in_test`Source