testable for seq and contramap (for testable)

CHANGES.md

@@ -1,3 +1,7 @@
+### unreleased
+
+- Add `seq`, a testable for `Seq.t` and `contramap` (#412 @xvw)
+
 ### 1.8.0 (2024-07-25)
 
 - Add `match_raises`, a generalized version of `check_raises`

src/alcotest-engine/test.ml

@@ -42,6 +42,10 @@ let testable (type a) (pp : a Fmt.t) (equal : a -> a -> bool) : a testable =
   end in
   (module M)
 
+let contramap f t =
+  let pp ppf = (Fmt.using f (pp t)) ppf and equal a b = equal t (f a) (f b) in
+  testable pp equal
+
 let int32 = testable Fmt.int32 ( = )
 let int64 = testable Fmt.int64 ( = )
 let int = testable Fmt.int ( = )
@@ -78,6 +82,15 @@ let list e =
   in
   testable (Fmt.Dump.list (pp e)) eq
 
+let seq e =
+  let rec eq s1 s2 =
+    match (Seq.uncons s1, Seq.uncons s2) with
+    | Some (x, xs), Some (y, ys) -> equal e x y && eq xs ys
+    | None, None -> true
+    | _ -> false
+  in
+  testable (Fmt.Dump.seq (pp e)) eq
+
 let slist (type a) (a : a testable) compare =
   let l = list a in
   let eq l1 l2 = equal l (List.sort compare l1) (List.sort compare l2) in

src/alcotest-engine/test.mli

@@ -74,6 +74,9 @@ val unit : unit testable
 val list : 'a testable -> 'a list testable
 (** [list t] tests lists of [t]s. *)
 
+val seq : 'a testable -> 'a Seq.t testable
+(** [seq t] tests sequence of [t]s. *)
+
 val slist : 'a testable -> ('a -> 'a -> int) -> 'a list testable
 (** [slist t comp] tests sorted lists of [t]s. The list are sorted using [comp]. *)
 
@@ -107,6 +110,10 @@ val neg : 'a testable -> 'a testable
 (** [neg t] is [t]'s negation: it is [true] when [t] is [false] and it is
     [false] when [t] is [true]. *)
 
+val contramap : ('b -> 'a) -> 'a testable -> 'b testable
+(** [contramap f t] lift a ['a testable] to a ['b testable],
+    converting ['b] to ['a]. *)
+
 (** {1 Assertion functions}
 
     Functions for asserting various properties within unit-tests. A failing