alcotest

by mirage

mirage / alcotest

A lightweight and colourful test framework

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Alcotest logo

Alcotest is a lightweight and colourful test framework.

Alcotest exposes 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 for details.

For information on contributing to Alcotest, see CONTRIBUTING.md.

OCaml-CI Build Status TravisCI Build Status docs

Examples

A simple example (taken from

examples/simple.ml
):

Generated by the following test suite specification:

(* 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.

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
): ``
shell
$ ./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 folder for more 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.:
$ ./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).

For instance:

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

let int = let doc = "What is your prefered 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:
$ 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:

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:

$ 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 qcheck does random generation and property testing (e.g. Quick Check)

  • crowbar and bun are similar to qcheck, but use compiler-directed randomness, e.g. it takes 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.

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