Alcotest exposes a simple interface to perform unit tests. It exposes
TESTABLE module type, a
check function to assert test
predicates and a
run function to perform a list of
unit -> unit
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.
A simple example (taken from
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  [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
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.
$ ./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
'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
which explains how to parse and serialize values of type
'a (note: do not
use positional arguments, only optional arguments are supported).
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] ]
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.
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.
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 ] ]
$ 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 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)
allows to write tests in the same file as your source-code; they
will be run only in a special mode of compilation.
with-test & >= "1.1.0"