in OCaml I can catch exceptions:
try some_fn () with | e -> print_endline "exception caught!"
but what about the other way around, detecting that a function does not throw an exception (when it should be)?
CodePudding user response:
I managed to write some very hacky way to achieve that: I create a wrapper around the function I want to test, which throws some specific exception at the end. I catch anything but that exception.
exception Finished
let check (fn : unit -> unit) =
let wrapper _ = (
fn ();
raise Finished)
in
try wrapper () with e when e <> Finished -> ()
in utop this works:
utop # check (fun _ -> ());;
Exception: Finished.
utop # check (fun _ -> failwith "hey");;
- : unit = ()
EDIT: my coworker suggested:
let should_fail fn =
if Result.try_with fn |> Result.is_ok then failwith "this test should fail"
CodePudding user response:
Exceptions can be handled within pattern matching cases, allowing very clean expression for this check:
match some_fn () with
| exception _ -> print_endline "exception caught!"
| _ -> print_endline "error: no exception raised!"
We can abstract this check into a function:
let throws_exception f =
match f () with
| exception _ -> true
| _ -> false
Which we can use in an assertion like so:
assert (throws_exception (fun () -> raise (Failure "msg")))