Add a test.

testsuite/tests/basic/maps.ml

@@ -27,5 +27,45 @@ let () =
   print_endline "Union+concat (with Map.union)";
   let f3 _ l r = if l = r then None else Some (l ^ r) in
   show (IntMap.union f3 m1 m2);
-
   ()
+
+let show m = IntMap.iter (fun k v -> Printf.printf "%d -> %d\n" k v) m
+
+let update x f m =
+  let yp = IntMap.find_opt x m in
+  let y = f yp in
+  match yp, y with
+  | _, None -> IntMap.remove x m
+  | None, Some z -> IntMap.add x z m
+  | Some zp, Some z -> if zp == z then m else IntMap.add x z m
+
+let () =
+  print_endline "Update";
+  let rec init m  = function
+    | -1 -> m
+    | n -> init (IntMap.add n n m) (n - 1)
+  in
+  let n = 9 in
+  let m = init IntMap.empty n in
+  for i = 0 to n + 1 do
+    for j = 0 to n + 1 do
+      List.iter (function (k, f) ->
+          let m1 = update i f m in
+          let m2 = IntMap.update i f m in
+          if not (IntMap.equal ( = ) m1 m2 && ((m1 == m) = (m2 == m))) then begin
+            Printf.printf "ERROR: %s: %d -> %d\n" k i j;
+            print_endline "expected result:";
+            show m1;
+            print_endline "result:";
+            show m2;
+          end
+        )
+      [
+        "replace",                          (function None -> None   | Some _ -> Some j);
+        "delete if exists, bind otherwise", (function None -> Some j | Some _ -> None);
+        "delete",                           (function None -> None   | Some _ -> None);
+        "insert",                           (function None -> Some j | Some _ -> Some j);
+      ]
+    done;
+  done;
+;;

testsuite/tests/basic/maps.reference

@@ -8,3 +8,4 @@ Union+concat (with Map.union)
 0 AB
 3 X1
 5 X2
+Update