xapi-stdext-threads, test: use stable testing interface

Alcotest changed how match_raises to actually be reasonable instead of failing
when the mathing function returns true (note how is_oob expects a string with
two spaces)

This also highlights why matching strings in exception is a bad idea. Instead
raise a non-stringy exception and use polymorphic compare.

Signed-off-by: Pau Ruiz Safont <pau.ruizsafont@cloud.com>

Author: psafont

ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.ml

@@ -19,6 +19,8 @@ type 'a t = {default: 'a event; mutable size: int; mutable data: 'a event array}
 
 exception EmptyHeap
 
+exception OutOfBounds of int
+
 let create n default =
   if n <= 0 then
     invalid_arg "create"
@@ -61,7 +63,7 @@ let maximum h =
 let remove h s =
   if h.size <= 0 then raise EmptyHeap ;
   if s < 0 || s >= h.size then
-    invalid_arg (Printf.sprintf "%s: index %d out of bounds" __FUNCTION__ s) ;
+    raise (OutOfBounds s) ;
   let n = h.size - 1 in
   let d = h.data in
   let x = d.(n) in

ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq.mli

@@ -18,6 +18,8 @@ type 'a t
 
 exception EmptyHeap
 
+exception OutOfBounds of int
+
 val create : int -> 'a -> 'a t
 (** [create n default] creates an empty Imperative priority queue.
    The queue initially is initialized to store [n] elements.

ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/ipq_test.ml

@@ -18,14 +18,9 @@ module Ipq = Xapi_stdext_threads_scheduler.Ipq
 let test_out_of_index () =
   let q = Ipq.create 10 0 in
   Ipq.add q {Ipq.ev= 123; Ipq.time= Mtime_clock.elapsed ()} ;
-  let is_oob = function
-    | Invalid_argument s when String.ends_with ~suffix:"  out of bounds" s ->
-        true
-    | _ ->
-        false
-  in
   let oob_check n =
-    (Alcotest.match_raises "out of bound" is_oob @@ fun () -> Ipq.remove q n) ;
+    let oob = Ipq.OutOfBounds n in
+    (Alcotest.check_raises "out of bound" oob @@ fun () -> Ipq.remove q n) ;
     Alcotest.(check bool) "same value" false (Ipq.is_empty q)
   in
   oob_check 10 ;