A lightweight and colourful test framework.

Alcotest exposes a simple interface to perform unit tests. It exposes
a simple `TESTABLE` module type, a `check` function to assert test
predicates and a `run` function to perform a list of `unit -> unit`
test callbacks.

Alcotest provides a quiet and colorful output where only faulty runs
are fully displayed at the end of the run (with the full logs ready to
inspect), with a simple (yet expressive) query language to select the
tests to run. See [the manpage](./alcotest-help.txt) for details.

The API documentation can be found [here][docs]. For information on
contributing to Alcotest, see [CONTRIBUTING.md](./CONTRIBUTING.md).

[![OCaml-CI Build Status](https://img.shields.io/endpoint?url=https://ci.ocamllabs.io/badge/mirage/alcotest/main&logo=ocaml)](https://ci.ocamllabs.io/github/mirage/alcotest)
[![Alcotest Documentation](https://img.shields.io/badge/doc-online-blue.svg)][docs]

[docs]: https://mirage.github.io/alcotest/alcotest/Alcotest/index.html

### Examples

A simple example (taken from `examples/simple.ml`):

Generated by the following test suite specification:

```ocaml
(* Build with `ocamlbuild -pkg alcotest simple.byte` *)

(* A module with functions to test *)
module To_test = struct
  let lowercase = String.lowercase_ascii
  let capitalize = String.capitalize_ascii
  let str_concat = String.concat ""
  let list_concat = List.append
end

(* The tests *)
let test_lowercase () =
  Alcotest.(check string) "same string" "hello!" (To_test.lowercase "hELLO!")

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

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

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

(* Run it *)
let () =
  let open Alcotest in
  run "Utils" [
      "string-case", [
          test_case "Lower case"     `Quick test_lowercase;
          test_case "Capitalization" `Quick test_capitalize;
        ];
      "string-concat", [ test_case "String mashing" `Quick test_str_concat  ];
      "list-concat",   [ test_case "List mashing"   `Slow  test_list_concat ];
    ]
```

The result is a self-contained binary which displays the test
results. Use `dune exec examples/simple.exe -- --help` to see the
runtime options.

Here's an example of a of failing test suite:

By default, only the first failing test log is printed to the console
(and all test logs are captured on disk). Pass `--show-errors` to
print all error messages.

### Using Alcotest with opam and Dune

Add `(alcotest :with-test)` to the `depends` stanza of your
`dune-project` file, or `"alcotest" {with-test}` to your opam file.
Use the `with-test` [package variable][with-test] to declare your
tests opam dependencies. Call opam to install them:

```sh-session
$ opam install --deps-only --with-test .
```

You can then [declare your test][tests] and link with Alcotest: `(test
(libraries alcotest …) …)`, and run your tests:

```sh-session
$ dune runtest
```

[with-test]: https://opam.ocaml.org/doc/Manual.html#pkgvar-with-test
[tests]: https://dune.readthedocs.io/en/stable/tests.html#custom-tests

### Selecting tests to execute

You can filter which tests to run by supplying a regular expression
matching the names of the tests to execute, or by passing a regular
expression _and_ a comma-separated list of test numbers (or ranges of
test numbers, e.g. `2,4..9`):

```sh-session
$ ./simple.native test '.*concat*'
Testing Utils.
[SKIP]     string-case            0   Lower case.
[SKIP]     string-case            1   Capitalization.
[OK]       string-concat          0   String mashing.
[OK]       list-concat            0   List mashing.
The full test results are available in `_build/_tests`.
Test Successful in 0.000s. 2 tests run.

$ ./simple.native test 'string-case' '1..3'
Testing Utils.
[SKIP]     string-case            0   Lower case.
[OK]       string-case            1   Capitalization.
[SKIP]     string-concat          0   String mashing.
[SKIP]     list-concat            0   List mashing.
The full test results are available in `_build/_tests`.
Test Successful in 0.000s. 1 test run.
```

Note that you cannot filter by test case name (i.e. `Lower case` or
`Capitalization`), you must filter by test name & number instead.

See the [examples][] directory for more examples.

[examples]: https://github.com/mirage/alcotest/tree/main/examples

### Quick and Slow tests

In general you should use `` `Quick`` tests: tests that are ran on any
invocations of the test suite. You should only use `` `Slow`` tests
for stress tests that are ran only on occasion (typically before a
release or after a major change). These slow tests can be suppressed
by passing the `-q` flag on the command line, e.g.:

```sh-session
$ ./test.exe -q # run only the quick tests
$ ./test.exe    # run quick and slow tests
```

### Passing custom options to the tests

In most cases, the base tests are `unit -> unit` functions. However,
it is also possible to pass an extra option to all the test functions
by using `'a -> unit`, where `'a` is the type of the extra parameter.

In order to do this, you need to specify how this extra parameter is
read on the command-line, by providing a [Cmdliner term][] for
command-line arguments which explains how to parse and serialize
values of type `'a` (*note:* do not use positional arguments, only
optional arguments are supported).

[Cmdliner term]: https://erratique.ch/software/cmdliner/doc/Cmdliner/Term/index.html

For instance:

```ocaml
let test_nice i = Alcotest.(check int) "Is it a nice integer?" i 42

let int =
  let doc = "What is your preferred number?" in
  Cmdliner.Arg.(required & opt (some int) None & info ["n"] ~doc ~docv:"NUM")

let () =
  Alcotest.run_with_args "foo" int [
    "all", ["nice", `Quick, test_nice]
  ]
```

Will generate `test.exe` such that:

```sh-session
$ test.exe test
test.exe: required option -n is missing

$ test.exe test -n 42
Testing foo.
[OK]                all          0   int.
```

### Lwt

Alcotest provides an `Alcotest_lwt` module that you could use to wrap
Lwt test cases. The basic idea is that instead of providing a test
function in the form `unit -> unit`, you provide one with the type
`unit -> unit Lwt.t` and alcotest-lwt calls `Lwt_main.run` for you.

However, there are a couple of extra features:

- If an async exception occurs, it will cancel your test case for you
  and fail it (rather than exiting the process).

- You get given a switch, which will be turned off when the test case
  finishes (or fails). You can use that to free up any resources.

For instance:

```ocaml
let free () = print_endline "freeing all resources"; Lwt.return ()

let test_lwt switch () =
  Lwt_switch.add_hook (Some switch) free;
  Lwt.async (fun () -> failwith "All is broken");
  Lwt_unix.sleep 10.

let () =
  Lwt_main.run @@ Alcotest_lwt.run "foo" [
    "all", [
      Alcotest_lwt.test_case "one" `Quick test_lwt
    ]
  ]
```

Will generate:

```sh-session
$ test.exe
Testing foo.
[ERROR]             all          0   one.
-- all.000 [one.] Failed --
in _build/_tests/all.000.output:
freeing all resources
[failure] All is broken
```

### Comparison with other testing frameworks

The README is pretty clear about that:

> Alcotest is a lightweight and colourful test framework.

Alcotest is the only testing framework using colors!

More seriously, Alcotest is similar to [ounit][] but it fixes a few of
the problems found in that library:

- Alcotest has a nicer output, it is easier to see what failed and
  what succeeded and to read the log outputs of the failed tests;

- Alcotest uses combinators to define pretty-printers and comparators
  between the things to test.

Other nice tools doing different kind of testing also exist:

- [qcheck][] does random generation and property testing (e.g. Quick
  Check);

- [crowbar][] and [bun][] are similar to qcheck, but use
  compiler-directed randomness, i.e. they take advantage of the AFL
  support the OCaml compiler;

- [ppx_inline_tests][] allows to write tests in the same file as
  your source-code; they will be run only in a special mode of
  compilation.

[ounit]: https://github.com/gildor478/ounit
[qcheck]: https://github.com/c-cube/qcheck
[crowbar]: https://github.com/stedolan/crowbar
[bun]: https://github.com/yomimono/ocaml-bun
[ppx_inline_tests]: https://github.com/janestreet/ppx_inline_test
