Add new Alcotest.suite function to make writing tests easier

[yawaramin]

Fixes #126.

[yawaramin]

The ocamlformat settings don't like the formatting of this example. IMHO, the format settings are incorrect :-)

[samoht]

Many thanks for your patch - two remarks:

• I really like using functions in the API instead of exposing concrete types. It's probably too late to make those types abstract as it will break every existing code, but let's start by exposing proper constructors first and see how adoption goes.
• I am not convinced by inlining all the test cases in "heavy" functions. Would you mind doing the minimum possible changes in the examples to keep the test functions separate (when they are big enough like they are right now) and avoid the heavyweight begin fun () -> ... end forms when possible?

[yawaramin]

Hi @samoht thanks for the review. Regarding your points,

• Agreed
• Do you mean like e.g.:

let string_case_lower_case () =
  Alcotest.(check string) "same string" "hello!" (To_test.lowercase "hELLO!")

let string_case_capitalization () =
  Alcotest.(check string) "same string" "World." (To_test.capitalize "world.")

let string_concat_string_mashing () =
  Alcotest.(check string) "same string" "foobar" (To_test.str_concat ["foo"; "bar"])

let list_concat_list_mashing () =
  Alcotest.(check (list int)) "same lists" [1; 2; 3] (To_test.list_concat [1] [2; 3])

let () =
  Alcotest.suite "Utils" begin fun group ->
    group "string-case" begin fun case ->
      case "Lower case" string_case_lower_case;
      case "Capitalization" string_case_capitalization;
    end;

    group "string-concat" begin fun case ->
      case "String mashing" string_concat_string_mashing;
    end;

    group "list-concat" begin fun case ->
      case ~speed:`Slow "List mashing" list_concat_list_mashing;
    end;
  end

Wouldn't this bring us back to the current situation where the test implementations and registrations are separate and can get out of sync? E.g. if I don't have an empty .mli and delete one of the cases, I could forget to delete its implementation.

EDIT: also this means we need to decide on names for the test case functions, and they have to be reasonable and meaningful names. We can't just do e.g. let f1 () = .... So we are very likely saving quite a bit of naming decision-making and verbosity by just inlining the lambdas as fun () -> .... I think that's a win for users.

[lessp]

Love this! Can we expect this to go in?