The ortac-runtime library provides support for the code generated by the various Ortac plugins.
Ortac (OCaml Runtime Assertion Checking) is a tool to turn executable Gospel specifications into code to test they hold.
Published: 26 Oct 2023
ortac — OCaml RunTime Assertion Checking
ortac is a tool to convert an OCaml module interface with Gospel specifications into code to check those specifications.
There are various ways to check specifications, all provided by plugins.
The QCheck-STM plugin generates a program using QCheck-STM that will test the module by running random functions calls and checking they give consistent results with the model provided in the Gospel specification; see the dedicated README for details.
This repository also contains two other experimental plugins, that are not yet stable. Expect rough edges if you venture to try them out:
the wrapper plugin generates wrapper modules, i.e. modules exposing the original interface but instrumenting all function calls with assertions on arguments and on results, either normal or exceptional; see the dedicated README for details,
At its core, Ortac provides a way to convert the executable fragment of Gospel into OCaml code. This core functionality is used by all plugins.
The easiest way to try
ortac out is to
opam pin it:
opam pin add -y https://github.com/ocaml-gospel/ortac.git
This repository contains the following OPAM packages:
ortac-core.opamwhich provides the
ortaccommand-line tool and the core functionality used by all plugins,
ortac-runtime.opamwhich provides the support library for the code generated by Ortac plugins,
ortac-qcheck-stm.opamwhich provides the QCheck-STM plugin for the
It also contains the following experimental packages:
ortac-wrapper.opamwhich provides the wrapper plugin for the
ortac-monolith.opamwhich provides the Monolith plugin for the
ortac-runtime-monolith.opamwhich provides the support library for the code generated with the Monolith plugin.
You can install only some of those packages by explicitly mentioning which package you want to install, for instance:
$ opam pin add ortac-core https://github.com/ocaml-gospel/ortac.git
To check that it is correctly installed, simply run
ortac. If you installed all packages, you should get:
ortac: required COMMAND name is missing, must be one of 'monolith', 'qcheck-stm' or 'wrapper'.
Usage: ortac COMMAND …
Try 'ortac --help' for more information.
or: How to use Ortac to test whether the specifications of a module hold.
The QCheck-STM plugin can generate a standalone executable that will test the consistency between the behaviour of the functions of the module and their model, as provided by the Gospel specifications. Look at the dedicated README for the QCheck-STM plugin to see how it can be used.
The Monolith plugin can generate a standalone executable that will try to falsify the Gospel specifications of a module by stress-testing the code. Look in the dedicated README for the Monolith plugin to see how it can be used.
The wrapper plugin can be used to generate a wrapper module that will expose the same interface as the original module but instrumenting all function calls with assertions corresponding to the Gospel specifications. Look in the dedicated README for the wrapper plugin to see how it can be used.
The main general limitation on what Gospel specifications are supported comes from the translation from Gospel into OCaml: it is only possible to translate the executable fragment of the Gospel language. In particular, it does not support quantifications except in the very specific patterns in which they quantify over an integer within explicit bounds such as:
forall i. a < i < b -> ...
exists i. a < i < b /\ ...
(the pattern matching tolerates some small variations in the way bounds are stated, such as
b >= i > a, etc. but not much more).
Additionally, each plugin has its own set of constraints on what it can handle. See the dedicated READMEs for details.