recipes.md

title	OCaml recipes for Codewars
tags	authoring recipe ocaml

Informative assertion messages

Default assertion messages of OCaml OUnit are usually very bad. OUnit assertons accept two optional, named arguments:

• ~printer, used to stringify values presented by assertion messages.
• ~msg, used to provide additional information about failure, if necessary.

With both arguments used, test output becomes more explicit:

"(square 3) should return 9" >:: (fun _ ->
  let actual = square 3 in
  assert_equal 9 actual ~printer: string_of_int ~msg: "Incorrect answer for n=3"
)

Tests for square
    (square 3) should return 9
        Incorrect answer for n=3
        expected: 9 but got: 10
    Completed in 0.22ms
Completed in 0.24ms

References

• Improving OUnit Output
• OUnit: xUnit testing framework for OCaml