package core

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package core
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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
val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
val (>>|) : 'a t -> ('a -> 'b) -> 'b t
module Monad_infix : sig ... end
val bind : 'a t -> f:('a -> 'b t) -> 'b t
val return : 'a -> 'a t
val map : 'a t -> f:('a -> 'b) -> 'b t
val join : 'a t t -> 'a t
val ignore_m : 'a t -> unit t
val all : 'a t list -> 'a list t
val all_unit : unit t list -> unit t
module Let_syntax : sig ... end
val of_thunk : (Base.Unit.t -> 'a) -> 'a t
val force : 'a t -> 'a
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