Module Tezt


Tezt (pronounced "tezty", as in "tasty" with a "z") is a test framework for OCaml. It is well suited for writing and executing unit, integration and regression tests. It integrates well with continuous integration (CI).

Tezt provides a function (Test.register) to register tests. Tests have a title, some tags, and an implementation (a function). Titles and tags can be used on the command-line to select which tests to run. The name of the file in which the test was registered can also be used to do so. The implementation of the test is ran if the test is selected. If this implementation does not raise an exception (for instance by calling, the test is considered to be successful. Along with modules Base, which is supposed to be opened a la Pervasives and which provides a few useful generic functions, and Check, which provides ways to perform assertions with nice error messages, the result is a framework that is suitable for unit tests.

Tests can be ran in a CI, optionally producing JUnit reports. Tezt can automatically compute a partition of the set of tests where subsets are balanced to take roughly the same amount of time to run. The intent is that each of those subset can be one CI job, resulting in automatic balanced parallelisation.

Specific features supporting integration tests include:

Specific features supporting regression tests include:

Tezt provides a flexible user interface:

To get started, register tests with Test.register, then call the main function Tests are run from the command-line, for instance with dune runtest or dune exec. The latter gives access to a large list of command-line options to select which tests to run and how. Execute your program with --help to get the list. See also the Tezt mini-tutorial.


Tezt executables can be compiled to bytecode, native code, or JavaScript. This is reflected by three Dune libraries:

Function is only available in tezt and tezt.js. In other words, to actually run the tests you have to decide whether to use the JavaScript backend or not.

The difference between tezt and tezt.js is that tezt.js does not provide:

If you want to run your tests on multiple backends you have to write two executables: one linked with tezt and one linked with tezt.js. To share the code of your tests, you can write your calls to Test.register in a library that depends on tezt.core. Here is an example of dune files:

; Dune file for the library that calls [Test.register].
 (name tezts)
 (libraries tezt.core)
 (library_flags (:standard -linkall))
 (flags (:standard) -open Tezt_core -open Tezt_core.Base))

; Dune file for the executable used to run tests in native or bytecode mode.
(executable (name main) (libraries tezts tezt))

; Dune file for the executable used to run tests using nodejs.
(executable (name main_js) (modes js) (libraries tezts tezt.js))


module Background = Tezt_core.Background

Support for running promises in the background.

module Base = Tezt_core.Base

Base primitives useful in writing tests.

module Check = Tezt_core.Check

Support for expressing assertions.

module Cli = Tezt_core.Cli

Command-line interface options.

module Diff = Tezt_core.Diff

Compute the difference between two sequences of items.

module JSON = Tezt_core.JSON

JSON handling (encoding/decoding, accessors, error management, etc).

module Log = Tezt_core.Log

Functions for logging messages.

module Process : sig ... end

Managing external processes.

module Process_hooks = Tezt_core.Process_hooks

Process hooks, in particular for use with regression tests.

module Regression = Tezt_core.Regression

Regression test helpers (run tests, capture output, etc).

module Runner : sig ... end

Runner specifications for processes spawned remotely using SSH.

module Temp : sig ... end

Temporary file management.

module Test : sig ... end

Base test management (registering, initializations, etc).