Tezt: OCaml Tezos Test Framework

Tezt is a generic test framework written in OCaml. It focuses on integration tests that launch external processes. In particular, Tezt can be used to orchestrate tests involving Tezos nodes and clients.

To facilitate the use with Tezos, Tezt has been complemented by a specific library called Tezt-Tezos.

Tezt is pronounced /tɛzti/ (think “tezty”, as in Tez are tas*ty*).

The main benefits of using Tezt-Tezos are:

  • tests are written in the same language as Octez itself (OCaml), which reduces context switch for developers;

  • tests do not actively poll the node as they passively listen to node events instead, which results in faster and more reliable tests;

  • in verbose mode, logs show the interleaved output of all external processes, while the tests are running;

  • it should be easy to use and extend.

Therefore, Tezt and Tezt-Tezos have been leveraged to build a test suite for Octez. See tezt/README.md for details on its implementation.

The rest of this page explains how to run the test suite and how to add new tests.

How to Run Tests

It is recommended to set up an alias:

alias tezt='dune exec tezt/tests/main.exe --'

Try it with --help to get the list of command-line options as follows:

tezt --help

Just run tezt with no options to run all tests. However, most often you only want to run a subset of the tests. You can get the list of tests with --list:

tezt --list

For instance, to run only tests from files basic.ml and RPC_test.ml that have tag alpha but not tag regression, with log level “info”, run:

tezt -f basic.ml -f RPC_test.ml alpha /regression -i

You can also run tests in parallel, although in that case it is recommended to use the default log level to avoid interleaving logs. For instance, the following command runs tests declared in file encoding.ml with up to 8 tests in parallel:

tezt -f encoding.ml -j 8

How to Write New Integration Tests

The best way to get started is to have a look at existing tests in directory tezt/tests of the Octez repository.

Most integration tests are part of the same executable tezt/tests/main.exe. The source of this module is tezt/tests/main.ml. This executable runs all tests, but you can restrict the set of tests to run by specifying tags on the command line, or even the titles of the tests to run (with the --test option).

All tests do not have to be implemented in tezt/tests/main.ml though. You can of course add more modules and have them be linked into main.exe together. The best way to do this is to write your tests as functions and call them from the main module.

For instance, let’s create a new basic test in a new file named tezt/tests/basic.ml:

let check_node_initialization (history_mode : Node.history_mode) :
    Protocol.t list -> unit =
      (sf "node initialization (%s mode)" (Node.show_history_mode history_mode))
    ~tags:["basic"; "node"; Node.show_history_mode history_mode]
  @@ fun protocol ->
  let metrics_addr = "localhost" in
  let metrics_port = Port.fresh () in
  let* node =
    Node.init [History_mode history_mode] ~metrics_addr ~metrics_port
  let* client = Client.init ~endpoint:(Node node) () in
  let* () = Client.activate_protocol ~protocol client in
  Log.info "Activated protocol." ;
  let* () = repeat 10 (fun () -> Client.bake_for_and_wait client) in
  Log.info "Baked 10 blocks." ;
  let* level = Node.wait_for_level node 11 in
  Log.info "Level is now %d." level ;
  let* identity = Node.wait_for_identity node in
  if identity = "" then Test.fail "identity is empty" ;
  Log.info "Identity is not empty." ;
  let addr = Format.sprintf "http://%s:%d/metrics" metrics_addr metrics_port in
  let* metrics =
    Process.spawn ~log_output:false "curl" ["-s"; addr]
    |> Process.check_and_read_stdout
  if metrics = "" then Test.fail "Unable to read metrics" else return ()

let register ~protocols =
  check_node_initialization Archive protocols ;
  check_node_initialization (Full None) protocols ;
  check_node_initialization (Rolling None) protocols

Then, let’s launch the test from tezt/tests/main.ml by calling:

Basic.register ~protocols:[Alpha] ;
Test.run () (* This call should already be there. *)

Finally, let’s try it with:

dune exec tezt/tests/main.exe -- basic --info

The --info flag allows you to see the Log.info messages. It is the same as -i. Here is what you should see:

$ dune exec tezt/tests/main.exe -- basic --info
[13:45:36.666] Starting test: Alpha: node initialization (archive mode)
[13:45:37.525] Activated protocol.
[13:45:38.215] Baked 10 blocks.
[13:45:38.215] Level is now 11.
[13:45:38.215] Identity is not empty.
[13:45:38.231] [SUCCESS] (1/3) Alpha: node initialization (archive mode)
[13:45:38.231] Starting test: Alpha: node initialization (full mode)
[13:45:39.113] Activated protocol.
[13:45:39.813] Baked 10 blocks.
[13:45:39.813] Level is now 11.
[13:45:39.813] Identity is not empty.
[13:45:39.828] [SUCCESS] (2/3) Alpha: node initialization (full mode)
[13:45:39.828] Starting test: Alpha: node initialization (rolling mode)
[13:45:40.708] Activated protocol.
[13:45:41.407] Baked 10 blocks.
[13:45:41.407] Level is now 11.
[13:45:41.407] Identity is not empty.
[13:45:41.422] [SUCCESS] (3/3) Alpha: node initialization (rolling mode)

Detailed Walk through the Basic Test

Let’s review what our basic test in the previous section does.

  • First, note that the Tezt library and its Base module are opened automatically by Dune based on its configuration file. The Base module contains useful functions such as let* (which is Lwt.bind) or sf (a short-hand for Printf.sprintf).

  • Then, we define a function check_node_initialization which registers one test. It is parameterized by the history mode. Protocol.register_test is partially applied here; check_node_initialization is also implicitly parameterized by the list of protocols to run the test on.

  • The function Protocol.register_test registers a test. It is a wrapper over Test.register. This wrapper is preferred when the test is parameterized by a list of protocols. The ~__FILE__ argument gives the source filename so that one can select this file with the --file argument, to only run tests declared in this file. Each test has a title which is used in logs and on the command-line with the --test option (which allows to run a particular test from its title). Each test also has a list of tags. We gave our test the tag basic in particular. No other test has this tag, so it is easy to run all of the tests of our new Basic module, and only them, by adding basic on the command-line.

  • The function Protocol.register_test takes a function as an argument. This function contains the implementation of the test.

  • First, we initialize a node with Node.init. This creates a node and runs the node command identity generate, then config init and finally run. It then waits until the node is ready, and returns the node. Note that you do not have to call Node.init. For instance, if you want to test the behavior of the node without an identity, you can call Node.create, followed by Node.config_init and Node.run.

  • Then, we initialize a client with Client.init. We give it a node, which is the node that the client will connect to by default. Note that we can still use this client to perform operations on other nodes if we want to, it’s just convenient to specify it once and for all.

  • Then, we activate the protocol with the activate protocol command of the client. By default, this activates the protocol given as argument, with some default parameters and using the default activator key (defined in the Constant module). This activator key was added to the client by Client.init. You can override all of this. For instance, if you don’t want the client to know the default activator key, use Client.create instead of Client.init (you can use Client.import_secret_key to import another activator key, for instance). Or, if you want to change the fitness or the parameter file, you can use the ?fitness and ?parameter_file optional arguments of Client.activate_protocol.

  • Then, we log a message using Log.info. This message is not visible with the default verbosity, but you can see it by running main.exe with the --info option (or --verbose).

  • Then, we repeat Client.bake_for 10 times, to bake 10 blocks.

  • Then, we wait for the level of the node to be at least 11 (the activation block plus the 10 blocks that we baked) using Node.wait_for_level. If you call this function and the level is already 11 or greater, Node.wait_for_level returns immediately. (Note: Node.wait_for_level makes the test fail if the node stops before reaching level 11.)

  • Finally, we read the identity of the node using Node.wait_for_identity which returns as soon as the node reads the identity file. In fact, this was probably done much sooner, but Tezt stores the identity in case you try to query it later, just like the level. (Note: Node.wait_for_identity makes the test fail if the node stops before reading the identity file.)

  • We check that the identity is not empty, and if it is we call Test.fail. This causes the test to terminate immediately with an error. Note that it is not the only cause of failure for this test: we already saw that Node.wait_for_level and Node.wait_for_identity can cause a test failure, and if anything goes wrong (failing to initialize the node or the client, failing to activate the protocol…) Test.fail is called automatically as well.

  • After the test succeeds or fails, Test.run cleans up everything. It terminates all running processes by sending SIGTERM. It waits for them with waitpid to avoid zombie processes. And it removes all temporary files, in particular the data directory of the node and the base directory of the client.

  • We run this test three times, once per history mode: archive, full and rolling. Note that we added the history mode as a tag to Test.register, so if we want to run only the test for history mode full, for instance, we can simply run dune exec tezt/tests/main.exe -- basic full. You can see our list of basic tests and their tags with dune exec tezt/tests/main.exe -- basic --list.

How to Write New Unit Tests

For Tezt, the main difference between a unit test and an integration test is that a unit test does not use the Process module. Indeed, an integration test tests an executable by running it, while a unit test links with a library to test its functions directly.

Since the scope of unit tests is much smaller, they are usually registered in executables that are dedicated to the library being tested. For instance, tests for src/lib_base could be put in an executable named src/lib_base/tezt/main.exe. Such executables are usually faster to compile and run than tezt/tests/main.exe since their dependency cone is limited.

To add unit tests to a library which does not yet have a Tezt executable, create files such as src/lib_base/tezt/example.ml and src/lib_base/tezt/other.ml and use Test.register to register tests in those files, at toplevel. Here is a minimal example:

let () =
    ~title:"test title here"
    ~tags:["test"; "tags"; "here"]
  @@ fun () ->
  (* your test here *)

Then, declare those files in manifest/main.ml:

let _octez_base_tezts =
    ["example"; "other"]

This causes the manifest to generate executable src/lib_base/tezt/main.exe for you. This executable calls Test.run. It also declares a Dune alias runtest so that you can run your tests with either of the following commands:

dune build @src/lib_base/runtest
dune exec src/lib_base/tezt/main.exe

Note that your tests will actually also be available in tezt/tests/main.exe. This executable gathers all tests so that the CI can auto-balance them.


If you want to be able to run your test with Node.js, declare them in the manifest with ~js_compatible:true and with JS in ~modes. For instance:

let _octez_base_tezts =
    ["example"; "other"]
    ~modes:[Native; JS]

Running dune build will generate not only a native executable (src/lib_base/tezt/main.exe) but also a JavaScript file (src/lib_base/tezt/main_js.bc.js) that you can run with Node.js:

nodejs _build/default/src/lib_base/tezt/main_js.bc.js

Note however that tests that use Tezt.Process, Tezt.Temp or Tezt.Runner cannot use the JavaScript backend. In other words, integration tests cannot be run with Node.js, only unit tests.

Regression Tests

Regression tests are used to prevent unintended changes to existing functionality by ensuring that the software behaves the same way as it did before introduced changes.

Regression tests capture commands and output of commands executed during a test. An output of some regression test is stored in the repository and is expected to match exactly with the captured output on subsequent runs. An added advantage of this is that when a change in behaviour is intentional, its effect is made visible by the change in test’s output.

To run all the regression tests, use the regression tag:

dune exec tezt/tests/main.exe regression

When the change in behaviour is intentional or when a new regression test is introduced, the output of regression test must be (re-)generated. This can be done with the --reset-regressions option, e.g.:

dune exec tezt/tests/main.exe regression -- --reset-regressions

Regression tests are registered with Regression.register instead of Test.register. Use Regression.capture or Regression.hooks to capture output that you want to be stable. Regression tests can be used both in unit tests and integration tests.

Pre-commit hook

The pre-commit hook located in scripts/pre_commit/pre_commit.py executes modified Tezt tests automatically. It looks for staged files (the default) or modified files (if --unstaged is passed) in tezt/tests and executes them. This avoids pushing commits that will break the CI. It is also handy to execute the relevant subset of tests by calling ./scripts/pre_commit/pre_commit.py [--unstaged] manually.

We refer to the header of pre_commit.py and its --help flag for additional instructions.