Overview of Testing in Octez#

The goal of this document is to give an overview on how testing is done in Octez, and to help Octez contributors use the test suite and write tests by pointing them towards the most appropriate testing framework for their use case. Finally, this guide explains how tests can be run automatically in the Octez CI and how to measure test coverage.

The frameworks used in Octez can be categorized along two axes: the type of component they test, and the type of testing they perform. We distinguish the following components:

  • Node

    • Protocol

      • Michelson interpreter

      • Stitching

  • Networked nodes

  • Client

  • Ledger application

  • Baker

Secondly, these components can be tested at different levels of granularity. Additionally, tests can verify functionality, but also non-functional properties such as performance (execution time, memory and disk usage). We distinguish:

Unit testing

Unit testing tests software units, typically functions, in isolation.

Integration testing

Integration testing tests compositions of smaller units.

System testing

System testing tests the final binaries directly.

Regression testing

In general, regression testing aims to detect the re-introduction of previously identified bugs. It can also refer to a coarse-grained type of testing where the output of a test execution is compared to a pre-recorded log of expected output. We here use “regression testing” to refer to the second meaning.

Property testing / Fuzzing

Both property testing and fuzzing test code with automatically generated inputs. Property testing is typically used to ensure functional correctness, and gives the user more control over generated input and the expected output. Fuzzing is typically used to search for security weaknesses and often guides input generation with the goal of increasing test coverage.

Performance testing

Testing of non-functional aspects such as run-time, memory and disk usage.

Acceptance testing

Testing of the software in real conditions. It is usually slower, more costly and less amenable to automation than integration or system testing. It is often the final step in the testing process, performed before a release. However, in Octez, acceptance testing is decoupled from releases, and currently consists in manually running a net of resilience tests on a regular base. These tests use various testing frameworks.

By combining the two axes, we obtain the following matrix. Each cell contains the frameworks appropriate for the corresponding component and testing type. The frameworks are linked to a sub-section of this page where the framework is presented in more detail.

Testing frameworks and their applications in Octez. EXP: Ppx_expect, AT: Alcotezt, QC: QCheck, TZ: Tezt, LTF: Long Tests and Performance regression Test Framework#














– Protocol



– – Michelson interpreter









Networked nodes




Testing frameworks#


Ppx_expect is a framework for writing tests for OCaml code generating textual output, similar to Cram which is used for testing command line applications.

Typical use cases:
  • Unit tests and integration tests leveraging existing printers instead of checking properties.

  • Tests that change on purpose over time. One can easily make tests pass again with a single dune invocation dune runtest --auto-promote

Example tests:


QCheck is a library for property-based testing in OCaml.

Typical use cases:
  • Verifying input-output invariants for functions with randomized inputs.

Example test:
  • QCheck is used in src/lib_base/test/test_time.ml to test the Tezos_base.Time module. For instance, subtracting and then adding a random amount of seconds to a random time should give back the original time: this tests that add and diff are consistent (and the inverse of each other). To run this test, you need to run dune exec src/lib_base/test/test_time.exe.



Tezt is a system testing framework for Octez. Tezt is capable of regression testing. Tezt focuses on tests that run in the CI, although it is also used for some manual tests (see the tezt/manual_tests folder). Its main strengths are summarized in its section in the Tezos Developer Documentation. Conceptually Tezt consists of a generic framework for writing tests interacting with external processes, and a set of Octez-specific modules for interacting with the Octez binaries: the client, baker, etc.

Typical use cases:
  • Testing the commands of octez-client. This allows to test the full chain: from client, to node RPC to the implementation of the economic protocol.

  • Test networks of nodes, with daemons.

  • Detecting unintended changes in the output of a component, using regression tests.

Example tests:

Long Tests and Performance regression Test Framework#

A library called tezt-performance-regression, which is a wrapper around Tezt, is used for tests that are too long to run in the CI and for performance testing. Those tests are run on dedicated machines and can send data points to an InfluxDB instance to produce graphs using Grafana and/or detect performance regressions. See Tezt: Long Tests and Performance Regression Test Framework.


Alcotezt is an Alcotest-compatible wrapper for Tezt. With it, unit tests originally written for Alcotest (now deprecated) can be executed using Tezt instead. We are currently in the progress of migrating all Alcotests to Tezt, and we are using Alcotezt as a stop gap towards this goal. For new unit and integration testing suites, prefer using Tezt directly.

Typical use cases:
  • Conversion of pre-existing Alcotests to Tezt

Example tests:
  • Unit tests for tezos-clic . To execute them locally, run dune build @src/lib_clic/runtest.

  • Unit tests for octez-version. To execute them locally, run dune build @src/lib_version/runtest.

See Alcotezt: An Alcotest Compatibility Wrapper for Tezt for more information on how to convert tests to Alcotezt, and how to execute them.

Alcotest (usage deprecated)#

Alcotest is a library for unit and integration testing in OCaml. Alcotest was historically the primary tool in Octez for unit and integration testing of OCaml code. However, we are currently migrating to Tezt for unit, integration and system testing. To ease migration from Alcotest to Tezt, the Alcotezt wrapper was introduced. Alcotezt is briefly described above and in more detail in Alcotezt: An Alcotest Compatibility Wrapper for Tezt. The below Alcotest description applies to tests that have not yet been converted to Alcotezt.

Typical use cases:
  • Verifying simple input-output specifications for functions with a hard-coded set of input-output pairs.

  • OCaml integration tests.


Executing tests locally#

Whereas executing the tests through the CI, as described below, is the standard and most convenient way of running the full test suite, they can also be executed locally.

All tests can be run with make test in the project root. However, this can take some time, and some tests are resource-intensive or require additional configuration. Alternatively, one can run subsets of tests identified by a specialized target test-*. For instance, make test-unit runs the alcotest tests and should be quite fast. See the project Makefile for the full list of testing targets.

Measuring test coverage#

We measure test coverage with bisect_ppx. This tool is used to see which lines in the code source are actually executed when running one or several tests. Importantly, it tells us which parts of the code aren’t tested.

We describe here how bisect_ppx can be used locally. See below for usage with CI.

To install bisect_ppx, run the following command from the root of the project directory:

make build-dev-deps

The OCaml code should be instrumented in order to generate coverage data. This is done by prepending


to build and test commands run from the root of the project directory. For example,

./scripts/with_coverage.sh make
./scripts/with_coverage.sh make test-coverage

Generate the HTML report from the coverage files using

make coverage-report

The generated report is available in _coverage_report/index.html. It shows for each file, which lines have been executed at least once, by at least one of the tests.

Clean up coverage data (output and report) with:

make coverage-clean

The helper ./scripts/with_coverage.sh can also be used outside make commands (e.g. with dune, poetry). For example,

./scripts/with_coverage.sh dune runtest src/lib_shell/
./scripts/with_coverage.sh dune exec tezt/tests/main.exe -f basic.ml

However you launch the tests, the same commands are used to get the report (e.g. make coverage-report).

Enabling instrumentation for new libraries and executables#

To ensure that all libraries and executables are included in the coverage report, the following field should be added to all library and executable(s) stanzas in all dune files, e.g.:

  (name ...)
    (backend bisect_ppx)))

The manifest will add this stanza automatically unless ~bisect_ppx:false is specified.

This enables the conditional instrumentation of the compilation unit through the ./scripts/with_coverage.sh helper as described above.

Exempted from this rule are the dune files that belong to tests, developer utilities and old protocols. In particular:

  • benchmarks, e.g. src/lib_shell/bench/dune

  • bindings, e.g. src/lib_sapling/bindings/dune

  • test frameworks, e.g. tezt/lib/dune

  • test packages, e.g. src/*/test/dune

  • old protocols, e.g. src/proto_00*/*/*dune

  • helper utilities, e.g.:

    • src/openapi/dune, (executable name openapi)

    • src/lib_client_base/gen/dune (executable name bip39_generator)

    • src/lib_protocol_compiler/dune (executable name replace)

    • src/proto_alpha/lib_parameters/dune (executable name gen)

    • src/proto_011_PtHangz2/lib_parameters/dune (executable name gen)

    • src/lib_protocol_environment/ppinclude/dune (executable name ppinclude)

    • src/lib_store/legacy_store/dune (executable name legacy_store_builder)

Truncated coverage files#

Occasionally, tests write corrupted coverage data. If you run into the issue, you will see a message like:

$ make coverage-report
Error: coverage file '_coverage_output/foobar.coverage' is truncated

make: *** [Makefile:105: coverage-report] Error 1


$ make coverage-report
bisect-ppx-report: internal error, uncaught exception:
                   Bisect_common.Invalid_file("_coverage_output/foobar.coverage", "unexpected end of file while reading magic number")

make: *** [Makefile:112: coverage-report] Error 125

Typically, this indicates that a instrumented binary that was launched by the test was terminated abruptly before it had time to finish writing coverage data. You can just rerun the test, and most likely, it won’t produce a corrupted trace on the second run. However, this is not a long-term solution. Below, we present some hints on how to debug this issue:

Binaries instrumented with bisect_ppx attach an at_exit handler that writes collected coverage data at termination of the tested process execution.

To ensure that this process is not disrupted, one should follow these guidelines:

For system test frameworks

System test frameworks like Tezt: OCaml Tezos Test Framework, run binaries e.g. octez-client and octez-node. Typically, they do so with calls to exec so the resulting process does not inherit the signal handlers from the parent process (the test framework). When writing tests in these frameworks, the author must ensure that the processes launched are instrumented and that they do proper signal handling: they should catch SIGTERM and call exit in their SIGTERM handler. This should already be the case for the binaries in octez. They should also ensure that the framework terminates the processes with SIGTERM.

For integration test frameworks

Some integration test frameworks, such as the lib_p2p test framework, spawn subprocesses through fork. These subprocesses inherit the signal handler of the parent process (the test framework). Such frameworks should themselves be instrumented and themselves do proper signal handling as described above. Bisect provides a convenience for doing so, through the --sigterm flag:

(preprocess (pps bisect_ppx --bisect-sigterm))

When enabled, it ensures that the instrumented process writes coverage data successfully on receiving SIGTERM. For an illustration of how to implement this, and the problem it resolves, see !3792.

General process handling

If possible, do not leave processes “hanging” in tests. Instead, use e.g. wait or Lwt.bind to ensure that processes get a chance to terminate before the full test terminates. For an illustration of how to implement this, and the problem it resolves, see !3691.

Comparing reports#

At times, it is convenient to compare two coverage reports. This can be used to ensure that coverage does not regress when e.g. migrating a test from one framework to another. We provide a fork of bisect_ppx with this functionality. It adds the command compare-html to bisect-ppx-report.


bisect-ppx-report compare-html -x x.coverage -y y.coverage

will create an HTML report comparing the coverage of in x.coverage and y.coverage. A limitation of this tool is that it assumes that only coverage has changed – not the underlying source files.

Executing tests through the GitLab CI#

To execute the tests on a merge request, the trigger job needs to be manually executed. To trigger it, go to the GitLab merge request page. Click the grey gear in the leftmost circle of the pipeline, then click the Play button. If necessary, Marge-bot will trigger the merge request pipeline before merging it. For instances, to see the latest runs of the CI, visit this page. You can click the status of a pipeline for more details.

The results of the test suite on terminated pipelines is presented on the details of the merge request page corresponding to the pipeline’s branch (if any). For more information, see the GitLab documentation on Unit test reports.

By default, the test of the CI runs the tests as a set of independent jobs that cluster the tests with a varying grain. This strikes a balance between exploiting GitLab runner parallelism while limiting the number of jobs per pipeline. The grain used varies slightly for different types of tests:

Tezt integration and regression tests

By default, Tezt tests are grouped in several batch jobs named tezt and are executed in merge request pipelines. According to the tags attached to them, the tests can be handled differently. The description of these tags can be found in src/lib_test/tag.mli.

The OCaml package tests (Alcotest & QCheck)

The OCaml package tests are regrouped in a set of jobs per protocol package, in addition to one job regrouping tests for remaining packages.

Adding tests to the CI#

When adding a new test that should be run in the CI (which should be the case for most automatic tests), you need to make sure that it is properly configured. The procedure for doing this depends on the type of test you’ve added:

Tezt integration and regression tests

New Tezt tests will be included automatically in the CI.

The OCaml package tests (Alcotest & QCheck)

Any tests located in a folder named src/**/test/ that are executed through dune runtest will be picked up automatically by the CI. No intervention is necessary.


For other types of tests, you need to manually modify the CI configuration. Please refer to the CI configuration’s README (ci/README.md) for more information.

Test coverage in merge requests#

Build and tests are instrumented with bisect_ppx in the CI for each merge request on Octez. To measure test coverage in the CI, it launches the job unified_job in stage test_coverage which generates the coverage report. They are stored as an HTML report that can be downloaded or browsed from the CI page upon completion of the job (see the Artifacts produced by the MR pipeline in the GitLab UI).

The summary report gives the merge request an overall test coverage percentage (displayed just next to the MR pipeline in the GitLab UI).

Additionally, using bisect-ppx-report cobertura, we produce and upload a Cobertura artifact activating the test coverage visualization in GitLab:


Known issues#

  1. After termination of the unified_coverage job, test coverage visualization can take some time to load. Once the coverage report is processed by GitLab, you will have to refresh the Changes tab of the MR to see the results.

  2. Instrumenting the code with both ppx_inline_test and bisect_ppx can produce misplaced locations. This is caused by a bug in ppx_inline_test version 0.14.1 that will be in their next release.

  3. Occasionally, tests write corrupted coverage data. In this case, the job unified_coverage will fail. We’ve done our best to ensure this happens rarely. If it happens, you can either try:

    • Re-running the full pipeline.

    • Reading the log of the job unified_coverage. It’ll direct you to the test job that produced the corrupted coverage file. You can then retry the test job, and once finished, retry the unified_coverage job.

    • Finally, if the problem persists, adding the label ci--no-coverage will disable the unified_coverage job. You can add this as a last resort to merge the MR.

Test coverage on master#

In addition to computing test coverage on merge request, we also associate coverage information to each merge commit on the master branch. Instead of running the test suite on master, which would be wasteful, we fetch it from the most recent merge request.

The job unified_coverage detects when it runs on master. In this case, it reads the history of the branch to find the latest pipeline on the most recently merged branch. It then fetches the coverage result from there, and also retrieves the artifacts which contains the HTML coverage report. GitLab also produces a graph of the coverage ratio over time.


Besides implementing tests, it is necessary to comment test files as much as possible to keep a maintainable project for future contributors. As part of this effort, we require that contributors follow this convention:

  1. For each unit test module, add a header that explains the overall goal of the tests in the file (i.e., tested component and nature of the tests). Such header must follow this template, and be added after license:

(** Testing
    Component:    (component to test, e.g. Shell, Micheline)
    Invocation:   (command to invoke tests)
    Dependencies: (e.g., helper files, optional so this line can be removed)
    Subject:      (brief description of the test goals)
  1. For each test in the unit test module, the function name shall start with test_ and one must add a small doc comment that explains what the test actually asserts (2-4 lines are enough). These lines should appear at the beginning of each test unit function that is called by e.g. Alcotest_lwt.test_case. For instance,

(** Transfer to an unactivated account and then activate it. *)
let test_transfer_to_unactivated_then_activate () =
  1. Each file name must be prefixed by test_ to preserve a uniform directory structure.

  2. OCaml comments must be valid ocamldoc special comments.

  3. If a test takes 2 minutes or more on the CI, it should be tagged as slow (see Tezt integration and regression tests). Note that tests with tag slow do not run automatically in the CI of merge requests.